29 results on '"Muraki, K."'
Search Results
2. Non-selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP.
- Author
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Beech DJ, Muraki K, and Flemming R
- Subjects
- Amino Acid Sequence, Animals, Drosophila, Drosophila Proteins chemistry, Drosophila Proteins genetics, Humans, Ion Channels chemistry, Ion Channels genetics, Molecular Sequence Data, Drosophila Proteins physiology, Ion Channels physiology, Muscle, Smooth physiology
- Abstract
Throughout the body there are smooth muscle cells controlling a myriad of tubes and reservoirs. The cells show enormous diversity and complexity compounded by a plasticity that is critical in physiology and disease. Over the past quarter of a century we have seen that smooth muscle cells contain--as part of a gamut of ion-handling mechanisms--a family of cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G-protein-coupled receptor activation, membrane stretch, intracellular Ca2+, pH, phospholipid signals and other factors. Progress in understanding the channels has, however, been hampered by a paucity of specific pharmacological agents and difficulty in identifying the underlying genes. In this review we summarize current knowledge of these smooth muscle cationic channels and evaluate the hypothesis that the underlying genes are homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2, and more are likely to be added soon. Some of these TRP proteins respond to a multiplicity of activation signals--promiscuity of gating that could enable a variety of context-dependent functions. We would seem to be witnessing the first phase of the molecular delineation of these cationic channels, something that should prove a leap forward for strategies aimed at developing new selective pharmacological agents and understanding the activation mechanisms and functions of these channels in physiological systems.
- Published
- 2004
- Full Text
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3. [Analyses of Ca-related ion channel currents and their involvement in Ca mobilization in smooth muscle and endothelial cells].
- Author
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Muraki K
- Subjects
- Animals, Chloride Channels metabolism, Cromakalim pharmacology, Endothelium cytology, Humans, Membrane Potentials drug effects, Nifedipine pharmacology, Palmitoylcarnitine physiology, Potassium Channels metabolism, Sphingosine physiology, Calcium metabolism, Calcium Channels physiology, Endothelium metabolism, Lysophospholipids, Muscle, Smooth metabolism, Sphingosine analogs & derivatives
- Abstract
Changes in intracellular Ca concentration ([Ca2+]i) play dominant roles in the regulation of ion channel activity. Thus, analyses of Ca-related ion channels, whose activation is responsible for and/or dependent on the changes in [Ca2+]i, are important to understand the physiological and pharmacological characteristics of smooth muscle cells (SMCs) and endothelial cells (ECs). We have clarified that, in SMCs, Ca mobilization by membrane depolarization and bioactive substances affects the activity of Ca-activated K (IK-Ca) and Cl channel currents. On the other hand, by measuring IK-Ca as an indicator of Ca mobilization, we found that palmitoylcarnitine (PC), a lipid released under ischemic conditions, mobilizes Ca in ECs via stimulation of endothelial differential gene (Edg) receptors. Moreover, sphingosine-1-phosphate, which is a lipid mediator and has a similar structure to PC, elevated [Ca2+]i in ECs via the activation of cation channels through Edg1 receptors. A myo-endothelial interaction is another regulatory factor of Ca mobilization in ECs as well as in SMCs. Nifedipine and levcromakalim, which have no effects on ion channels in ECs themselves, changed the membrane potential of ECs via a myo-endothelial pathway. These integral analyses provide better understanding of the functional roles of Ca-related ion channels and their involvement in Ca mobilization in SMCs and ECs.
- Published
- 2003
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4. Molecular and functional characterization of ERG, KCNQ, and KCNE subtypes in rat stomach smooth muscle.
- Author
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Ohya S, Asakura K, Muraki K, Watanabe M, and Imaizumi Y
- Subjects
- Animals, Anti-Arrhythmia Agents pharmacology, Antihypertensive Agents pharmacology, Blotting, Western, ERG1 Potassium Channel, Ether-A-Go-Go Potassium Channels, Gastric Fundus chemistry, Gene Expression physiology, Immunohistochemistry, Indapamide pharmacology, KCNQ Potassium Channels, KCNQ1 Potassium Channel, KCNQ2 Potassium Channel, KCNQ3 Potassium Channel, Male, Membrane Potentials drug effects, Membrane Potentials physiology, Muscle, Smooth chemistry, Patch-Clamp Techniques, Piperidines pharmacology, Polymerase Chain Reaction, Potassium Channels analysis, Pyloric Antrum chemistry, Pyridines pharmacology, RNA, Messenger analysis, Rats, Rats, Wistar, Cation Transport Proteins, Gastric Fundus physiology, Membrane Transport Proteins, Muscle, Smooth physiology, Potassium Channels genetics, Potassium Channels metabolism, Potassium Channels, Voltage-Gated, Pyloric Antrum physiology
- Abstract
Contribution of K(+) channels derived from the expression of ERG, KCNQ, and KCNE subtypes, which are responsible for rapidly and slowly activating delayed rectifier K(+) currents (I(Kr) and I(Ks), respectively) in cardiac myocytes, to membrane currents was examined in stomach circular smooth muscle cells (SMCs). The region-qualified multicell RT-PCR showed that ERG1/KCNE2 transcripts were expressed in rat stomach fundus and antrum SMCs and that KCNQ1/KCNE1 transcripts were expressed in antrum but not fundus. Western blotting and immunocytochemical analyses indicate that ERG1 proteins were substantially expressed in both regions, whereas KCNE1 proteins were faintly expressed in antrum and not in fundus. Both I(Kr)- and I(Ks)-like currents susceptible to E-4031 and indapamide, respectively, were identified in circular SMCs of antrum but only I(Kr)-like current was identified in fundus. It is strongly suggested that I(Kr)- and I(Ks)-like currents functionally identified in rat stomach SMCs are attributable to the expression of ERG1/KCNE2 and KCNQ1/KCNE1, respectively. The membrane depolarization by 1 microM E-4031 indicates the contribution of K(+) channels encoded by ERG1/KCNE2 to the resting membrane potential in stomach SMCs.
- Published
- 2002
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5. Local Ca(2+) transients and distribution of BK channels and ryanodine receptors in smooth muscle cells of guinea-pig vas deferens and urinary bladder.
- Author
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Ohi Y, Yamamura H, Nagano N, Ohya S, Muraki K, Watanabe M, and Imaizumi Y
- Subjects
- Aniline Compounds, Animals, Calcium metabolism, Cell Membrane metabolism, Fluorescent Dyes, Guinea Pigs, Immunohistochemistry, Kinetics, Large-Conductance Calcium-Activated Potassium Channel alpha Subunits, Large-Conductance Calcium-Activated Potassium Channels, Male, Membrane Potentials physiology, Microscopy, Confocal, Muscle, Smooth chemistry, Muscle, Smooth cytology, Patch-Clamp Techniques, Potassium Channels analysis, Ryanodine Receptor Calcium Release Channel analysis, Sarcoplasmic Reticulum metabolism, Xanthenes, Calcium Signaling physiology, Muscle, Smooth physiology, Potassium Channels physiology, Potassium Channels, Calcium-Activated, Ryanodine Receptor Calcium Release Channel physiology, Urinary Bladder cytology, Vas Deferens cytology
- Abstract
1. The relationship between Ca(2+) sparks spontaneously occurring at rest and local Ca(2+) transients elicited by depolarization was analysed using two-dimensional confocal Ca(2+) images of single smooth muscle cells isolated from guinea-pig vas deferens and urinary bladder. The current activation by these Ca(2+) events was also recorded simultaneously under whole-cell voltage clamp. 2. Spontaneous transient outward currents (STOCs) and Ca(2+) sparks were simultaneously detected at -40 mV in approximately 50 % of myocytes of either type. Ca(2+) sparks and corresponding STOCs occurred repetitively in several discrete sites in the subplasmalemmal area. Large conductance Ca(2+)-dependent K(+) (BK) channel density in the plasmalemma near the Ca(2+) spark sites generating STOCs was calculated to be 21 channels microm(-2). 3. When myocytes were depolarized from -60 to 0 mV, several local Ca(2+) transients were elicited within 20 ms in exactly the same peripheral sites where sparks occurred at rest. The local Ca(2+) transients often lasted over 300 ms and spread into other areas. The appearance of local Ca(2+) transients occurred synchronously with the activation of Ca(2+)-dependent K(+) current (I(K,Ca)). 4. Immunofluorescence staining of the BK channel alpha-subunit (BKalpha) revealed a spot-like pattern on the plasmalemma, in contrast to the uniform staining of voltage-dependent Ca(2+) channel alpha1C subunits along the plasmalemma. Ryanodine receptor (RyR) immunostaining also suggested punctate localization predominantly in the periphery. Double staining of BKalpha and RyRs revealed spot-like co-localization on/beneath the plasmalemma. 5. Using pipettes of relatively low resistance, inside-out patches that included both clustered BK channels at a density of over 20 channels microm(-2) and functional Ca(2+) storage sites were obtained at a low probability of approximately 5%. The averaged BK channel density was 3-4 channels microm(-2) in both types of myocyte. 6. These results support the idea that a limited number of discrete sarcoplasmic reticulum (SR) fragments in the subplasmalemmal area play key roles in the control of BK channel activity in two ways: (i) by generating Ca(2+) sparks at rest to activate STOCs and (ii) by generating Ca(2+) transients presumably triggered by sparks during an action potential to activate a large I(K,Ca) and also induce a contraction. BK channels and RyRs may co-localize densely at the junctional areas of plasmalemma and SR fragments, where Ca(2+) sparks occur to elicit STOCs.
- Published
- 2001
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6. SK4 encodes intermediate conductance Ca2+-activated K+ channels in mouse urinary bladder smooth muscle cells.
- Author
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Ohya S, Kimura S, Kitsukawa M, Muraki K, Watanabe M, and Imaizumi Y
- Subjects
- Animals, Calcium metabolism, Electrophysiology, In Vitro Techniques, Intermediate-Conductance Calcium-Activated Potassium Channels, Mice, Muscle, Smooth physiology, Potassium Channels genetics, RNA, Messenger metabolism, Reverse Transcriptase Polymerase Chain Reaction, Tissue Distribution, Urinary Bladder physiology, Muscle, Smooth metabolism, Potassium Channels metabolism, Potassium Channels, Calcium-Activated, Urinary Bladder metabolism
- Abstract
The single channel current of intermediate conductance Ca2 +-activated K+ channel (IK channel) was measured in mouse urinary bladder myocytes (MBM), and the molecular basis of the channel was suggested to be the SK4 subtype by RT-PCR. Among Ca2+-activated K+ channel subtypes (SK2, SK3, SK4 and BK), the mRNAs of SK4 and BK were predominantly expressed in MBM. IK channel currents recorded from MBM showed: 38.7 pS slope conductance under symmetrical 140 mM K+ conditions, Ca2+-dependent activation, and blockade by charybdotoxin and econazole. These results strongly suggest that SK4 encodes IK channels in MBM.
- Published
- 2000
- Full Text
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7. Cromakalim-induced membrane current in guinea-pig tracheal smooth muscle cells.
- Author
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Matsushita Y, Henmi S, Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Adenosine Triphosphate physiology, Animals, Dose-Response Relationship, Drug, Enzyme Inhibitors pharmacology, Guinea Pigs, Male, Membrane Potentials drug effects, Muscle, Smooth enzymology, Potassium pharmacology, Potassium Channel Blockers, Potassium Channels physiology, Protein-Tyrosine Kinases antagonists & inhibitors, Trachea enzymology, Bronchodilator Agents pharmacology, Cromakalim pharmacology, Muscle, Smooth drug effects, Muscle, Smooth physiology, Trachea drug effects, Trachea physiology
- Abstract
The characteristics of the cromakalim-induced membrane current were examined in single tracheal myocytes of the guinea-pig under voltage-clamp conditions. When K(+) concentrations in the pipette and bathing solutions were approximately 140 mM, cromakalim activated a membrane current (I(crom)) which was inward at -60 mV and reversed at -2 mV. I(crom) was blocked by 10 microM glibenclamide and potentiated when the ATP concentration in the pipette solution was decreased. The K(d) and Hill coefficient of glibenclamide for I(crom) block were 200 nM and 1.05, respectively. Application of the tyrosine kinase inhibitors, genistein and alpha-cyano-3-ethoxy-4-hydroxy-5-phenylthiomethylcinnamamid (ST638), reduced I(crom) in a concentration-dependent manner. Daidzein, which does not inhibit tyrosine kinase, was about 10 times less effective than genistein. Herbimycin A had no effect on I(crom). Internal application of these inhibitors from the pipette did not affect I(crom). In conclusion, cromakalim is a potent activator of the ATP-sensitive K(+) channel (K(ATP) channel) in guinea-pig tracheal myocytes. The inhibition of I(crom) by genistein and ST638 may be due to the direct block of the channel from outside.
- Published
- 2000
- Full Text
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8. Ca2+ images and K+ current during depolarization in smooth muscle cells of the guinea-pig vas deferens and urinary bladder.
- Author
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Imaizumi Y, Torii Y, Ohi Y, Nagano N, Atsuki K, Yamamura H, Muraki K, Watanabe M, and Bolton TB
- Subjects
- Action Potentials drug effects, Aniline Compounds, Animals, Calcium Channel Blockers pharmacology, Cell Membrane drug effects, Cell Membrane metabolism, Electric Stimulation, Electrophysiology, Fluorescent Dyes, Guinea Pigs, Image Processing, Computer-Assisted, In Vitro Techniques, Male, Membrane Potentials drug effects, Membrane Potentials physiology, Muscle, Smooth cytology, Muscle, Smooth drug effects, Patch-Clamp Techniques, Potassium Channel Blockers, Potassium Channels agonists, Urinary Bladder cytology, Urinary Bladder drug effects, Vas Deferens cytology, Vas Deferens drug effects, Xanthenes, Calcium metabolism, Muscle, Smooth metabolism, Potassium Channels metabolism, Urinary Bladder metabolism, Vas Deferens metabolism
- Abstract
1. Electrical events and intracellular calcium concentration ([Ca2+]) imaged using fluo-3 and laser scanning confocal microscopy were simultaneously monitored in single smooth muscle cells freshly isolated from guinea-pig vas deferens or urinary bladder. 2. Images obtained every 8 ms, during stepping from -60 to 0 or +10 mV for 50 ms under voltage clamp, showed that a rise in [Ca2+] could be detected within 20 ms of depolarization in five to twenty small (< 2 micrometer diameter) 'hot spots', over 95 % of which were located within 1.5 micrometer of the cell membrane. Depolarization at 30 s intervals activated hot spots at the same places. 3. Cd2+ or verapamil abolished both hot spots and Ca2+-activated K+ current (IK,Ca). Caffeine almost abolished hot spots and markedly reduced IK,Ca. Cyclopiazonic acid, which raised basal global [Ca2+], decreased the rise in hot spot [Ca2+] and IK,Ca amplitude during depolarization. These results suggest that Ca2+ entry caused Ca2+-induced Ca2+ release (CICR). 4. Under voltage clamp, hot spot [Ca2+] closely paralleled the rise in IK,Ca and reached a peak within 20 ms of the start of depolarization, but the rise in global [Ca2+] over the whole cell area was much slower. Step depolarization to potentials positive to -20 mV caused hot spots to grow in size and coalesce, leading to a rise in global [Ca2+] and contraction. Ca2+ hot spots also occurred during the up-stroke of an evoked action potential under current clamp. 5. It is concluded that the entry of Ca2+ in the early stages of an action potential evokes CICR from discrete subplasmalemma Ca2+ storage sites and generates hot spots that spread to initiate a contraction. The activation of Ca2+-dependent K+ channels in the plasmalemma over hot spots initiates IK,Ca and action potential repolarization.
- Published
- 1998
- Full Text
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9. Effects of ruthenium red on membrane ionic currents in urinary bladder smooth muscle cells of the guinea-pig.
- Author
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Hirano M, Imaizumi Y, Muraki K, Yamada A, and Watanabe M
- Subjects
- Animals, Caffeine pharmacology, Calcium Channels physiology, Delayed Rectifier Potassium Channels, Guinea Pigs, Ion Channels physiology, Large-Conductance Calcium-Activated Potassium Channels, Membrane Potentials drug effects, Muscle, Smooth cytology, Muscle, Smooth physiology, Patch-Clamp Techniques, Potassium Channel Blockers, Potassium Channels drug effects, Potassium Channels physiology, Urinary Bladder cytology, Urinary Bladder physiology, Ion Channels drug effects, Muscle, Smooth drug effects, Potassium Channels, Calcium-Activated, Potassium Channels, Voltage-Gated, Ruthenium Red pharmacology, Urinary Bladder drug effects
- Abstract
Three major ionic currents, Ca2+-dependent K+ current (IK-Ca), delayed rectifier type K+ current (Ikd) and Ca2+ current (ICa), were activated by depolarization under whole-cell clamp in single smooth muscle cells isolated from guinea-pig urinary bladder. Externally applied ruthenium red (RuR) reduced the amplitude of IK-Ca and ICa at 0 mV (IC50 values were 4.2 and 5.6 muM, respectively), but did not affect IKd. Spontaneous transient outward currents (STOCs) and caffeine-induced outward currents (Icaf) at -30 mV were reduced by external 10 muM RuR. When 10 muM RuR was added to the pipette solution, IK-Ca during depolarization, STOCs and Icaf significantly decreased with time. RuR did not change the unitary current amplitude of the large-conductance Ca2+-dependent K+ (BK) channels, but reduced the open probability of the channel under excised patch-clamp recording mode. RuR reduced the channel activity more effectively from the cytosolic face than from the other. This inhibition decreased when the cytosolic Ca2+ concentration was increased. These results indicate that RuR blocks BK and Ca2+ channels in urinary bladder smooth muscle cells. The decrease in IK-Ca, STOCs and Icaf by RuR is attributable to the direct inhibition of BK channel activity, probably in addition to the inhibition of Ca2+ release from storage sites. The direct inhibition of BK channel activity by RuR may be related to the interaction of RuR with the Ca2+-binding sites of the channel protein.
- Published
- 1998
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10. Comparative study of effects of isoproterenol and vasoactive intestinal polypeptide on voltage-dependent Ca2+ and Ca(2+)-activated K+ currents in porcine tracheal smooth muscle cells.
- Author
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Muraki K, Imaizumi Y, Bolton TB, and Watanabe M
- Subjects
- Animals, Calcium pharmacology, Calcium Channels drug effects, Calcium Channels physiology, Electrophysiology, Membrane Potentials drug effects, Membrane Potentials physiology, Muscle Relaxation drug effects, Muscle, Smooth physiology, Potassium physiology, Potassium Channels physiology, Swine, Trachea physiology, Adrenergic beta-Agonists pharmacology, Calcium physiology, Isoproterenol pharmacology, Muscle, Smooth drug effects, Potassium Channels drug effects, Trachea drug effects, Vasoactive Intestinal Peptide pharmacology
- Abstract
Effects of isoproterenol (Iso) and vasoactive intestinal polypeptide (VIP) on voltage-dependent Ca2+ channel (ICa) and Ca(2+)-activated K+ channel current (IK-Ca) in porcine tracheal smooth muscle cells were examined. When K+ currents were inhibited using a Cs-rich pipette solution, application of 0.1-1 microM Iso or 1-10 nM VIP increased ICa by 20-30%. On the other hand, IK-Ca elicited upon depolarization and spontaneous transient outward K+ currents (STOCs) recorded at a holding potential of -50 mV were enhanced by 80-100% in the presence of 0.1 microM Iso or 1 nM VIP.
- Published
- 1998
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11. Time course of Ca(2+)-dependent K+ and Cl- currents in single smooth muscle cells of guinea-pig trachea.
- Author
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Henmi S, Imaizumi Y, Muraki K, and Watanabe M
- Subjects
- Animals, Caffeine pharmacology, Calcium Channels metabolism, Central Nervous System Stimulants pharmacology, Electrophysiology, Guinea Pigs, Ion Channels physiology, Male, Membrane Potentials, Muscle, Smooth cytology, Muscle, Smooth drug effects, Patch-Clamp Techniques, Potassium Chloride pharmacology, Time Factors, Trachea, Calcium metabolism, Calcium Channels physiology, Muscle, Smooth metabolism
- Abstract
The time course of two types of Ca(2+)-dependent currents were compared in single smooth muscle cells freshly isolated from guinea-pig trachea. When the pipette solution contained mainly 140 mM KCl, depolarization from -60 mV to 0 mV evoked an initial inward current followed by an outward current which consisted of transient (I(to)) and sustained components. In addition, a long-lasting inward tail current (Itail) was occasionally observed after the repolarization to -60 mV. Although I(to) often occurred repetitively during depolarization, the first I(to) reached the peak of approximately 50 ms after the start of depolarization and had the largest amplitude in most cells examined. The amplitude of Itail increased with the increase in depolarization period up to about 500 ms. Pharmacological analyses indicate that I(to) and Itail are Ca(2+)-dependent K+ and Cl- currents (IK-Ca and ICl-Ca), respectively, and suggest that not only Ca(2+)-influx through Ca2+ channels but also subsequent Ca2+ release from stores contributes to activate these currents. Spontaneous transient outward and inward currents, IK-Ca and ICl-Ca, respectively, were simultaneously recorded at -40 mV. In over 80% of the spontaneous current events, outward and inward currents coupled one to one and always occurred in this order. Puff-application of 10 mM caffeine also induced IK-Ca and ICl-Ca in this order at -40 mV. When caffeine was applied twice with various intervals, the current amplitude in the second application depended upon the period of the interval. The recovery of ICl-Ca during the interval was faster than that of IK-Ca. The results indicate that the activation and decay time courses of ICl-Ca are slower but its recovery is faster than those of IK-Ca.
- Published
- 1996
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12. Characteristics of caffeine-induced and spontaneous inward currents and related intracellular Ca2+ storage sites in guinea-pig tracheal smooth muscle cells.
- Author
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Henmi S, Imaizumi Y, Muraki K, and Watanabe M
- Subjects
- Animals, Guinea Pigs, Male, Membrane Potentials drug effects, Muscle, Smooth cytology, Muscle, Smooth metabolism, Trachea drug effects, Caffeine pharmacology, Calcium metabolism, Muscle, Smooth drug effects
- Abstract
Characteristics of caffeine-induced inward current (Icaf) and spontaneous transient inward current were examined in single smooth muscle cells isolated from guinea-pig trachea. When a pipette solution contained mainly CsCl, an application of 10 mM caffeine elicited transient Icaf at a holding potential of -60 mV. Spontaneous transient inward currents were recorded in about 15% of cells examined and were abolished by caffeine. Both were Cl- current activated by an increase in intracellular Ca2+ concentration (ICl-Ca). When 10 mM caffeine was puff-applied twice with various intervals, the amplitude of the second Icaf depended upon the period of the interval. The relationship between the amplitude and the interval represents the recovery time course of Icaf, which was significantly slowed by 30 microM cyclopiazonic acid. The Icaf was not significantly affected by addition of Cd2+. Removal of external Ca2+ did not affect the first Icaf but markedly reduced the second one, regardless of the presence of Cd2+. In conclusion, Icaf is evoked by activation of ICl-Ca via Ca2+ release. The recovery time course of Icaf indicates the refilling of Ca2+ storage sites by the cyclopiazonic acid-sensitive Ca2+ pump. The refilling at -60 mV depends strongly upon Ca2+ influx through the Cd(2+)-insensitive pathway. Spontaneous transient inward currents may be also due to ICl-Ca activated by spontaneous Ca2+ release from local storage sites.
- Published
- 1995
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13. Effects of noradrenaline on membrane currents and action potential shape in smooth muscle cells from guinea-pig ureter.
- Author
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Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Action Potentials, Animals, Barium, Calcium Channels physiology, Electric Conductivity, Electrophysiology, Guanosine 5'-O-(3-Thiotriphosphate) pharmacology, Guanosine Diphosphate analogs & derivatives, Guinea Pigs, Heparin pharmacology, Intracellular Membranes drug effects, Intracellular Membranes physiology, Muscle, Smooth physiology, Patch-Clamp Techniques, Potassium Channels drug effects, Potassium Channels physiology, Sodium Channels drug effects, Sodium Channels physiology, Ureter cytology, Calcium Channels drug effects, Muscle, Smooth drug effects, Norepinephrine pharmacology
- Abstract
1. The effects of noradrenaline (NA) on action potential shape and underlying membrane currents were examined in single smooth muscle cells freshly isolated from the ureter of the guinea-pig. 2. The voltage-dependent Ca2+ current (ICa) elicited upon depolarization from -50 to 0 mV was reduced by 27% upon application of 10 microM NA. This reduction was inhibited or converted to potentiation by internal application of low molecular weight heparin or 5 mM EGTA, indicating that it may be mediated by Ca(2+)-dependent Ca2+ channel inactivation via inositol 1,4,5-trisphosphate production and subsequent Ca2+ release from intracellular Ca2+ storage sites. 3. In contrast, Ba2+ current (IBa) through Ca2+ channels was potentiated by 36% in the presence of 10 microM NA. Internal application of GTP gamma S made it difficult to remove potentiation of IBa by wash-out; internal application of GDP beta S abolished potentiation. 4. NA caused a greater reduction in the transient Ca(2+)-dependent K+ current (IK(Ca)) upon depolarization than it did in ICa. This reduction was inhibited by internally applied heparin, suggesting that the amount of releasable Ca2+ in the storage sites was markedly reduced in the presence of NA. The sustained component of IK(Ca) which gradually increased during depolarization was also reduced by NA. 5. Action potential duration, which was recorded in a standard solution containing Ca2+, was prolonged by the application of NA. 6. It can be concluded that Ca2+ channel activity in ureter smooth muscle cells is regulated by a dual mechanism: Ca(2+)-dependent inhibition and GTP-binding protein-mediated potentiation. Under physiological conditions, both ICa and IK(Ca) were reduced by NA but the reduction of IK(Ca) was much larger than that of ICa; this results in an increase in net inward current during the action potential plateau and prolongs the action potential.
- Published
- 1994
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14. Tetrahexylammonium ions increase Ca2+ sensitivity of contraction of guinea-pig ileal smooth muscle.
- Author
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Uyama Y, Muraki K, Walsh MP, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Biomechanical Phenomena, Calcimycin pharmacology, Calcium metabolism, Guinea Pigs, Inositol 1,4,5-Trisphosphate pharmacology, Male, Sarcoplasmic Reticulum physiology, Calcium pharmacology, Ileum physiology, Muscle Contraction physiology, Muscle, Smooth physiology, Quaternary Ammonium Compounds pharmacology
- Abstract
Effects of tetraalkylammonium ions, having tetraalkyl chains of increasing length from ethyl to octyl, on inositol-trisphosphate (InsP3)-induced Ca2+ release and contractile mechanics were examined in guinea-pig skinned ileal smooth muscle longitudinal strips. Although tetrahexylammonium ions (THexA) appeared to be the most potent inhibitor of Ca2+ release among the tetraalkylammonium ions examined, an additional and more prominent effect was found, i.e., the contraction induced by Ca2+ release showed a large sustained component in the presence of THexA. Potentiation of the contraction by THexA (above 30 microM) was also observed in skinned fibers in which the sarcoplasmic reticulum function was destroyed by treatment with A23187. The potentiating effect of THexA was the most potent by far among the tetraalkylammonium ions examined and was elicited by Ca(2+)-dependent and GTP-binding-protein-independent mechanisms. The potentiation was not due to activation of myosin light-chain kinase. The selective inhibitors of myosin light-chain kinase, protein kinase C and calmodulin reduced THexA-induced potentiation of contraction only at concentrations above 30 microM, at which non-specific effects are likely. Furthermore, relaxation induced by changing pCa from 4.5 to 8.5 was not affected by 1 mM THexA, suggesting that the potentiating effect is not mainly due to inhibition of myosin light-chain phosphatase. In conclusion, ThexA sensitizes guinea-pig skinned ileal smooth muscle to Ca2+ in a structure-selective manner. This sensitization appears not to be mediated mainly by a GTP-binding protein, by activation of myosin light-chain kinase or protein kinase C, by enhanced Ca2+ binding to calmodulin, or by inhibition of myosin light-chain phosphatase.
- Published
- 1994
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15. Effect of isoprenaline on Ca2+ channel current in single smooth muscle cells isolated from taenia of the guinea-pig caecum.
- Author
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Muraki K, Bolton TB, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Calcium Channels metabolism, Cecum metabolism, Cyclic AMP metabolism, Female, GTP-Binding Proteins metabolism, Guanosine 5'-O-(3-Thiotriphosphate) pharmacology, Guanosine Diphosphate analogs & derivatives, Guanosine Diphosphate pharmacology, Guinea Pigs, In Vitro Techniques, Kinetics, Male, Membrane Potentials physiology, Muscle, Smooth cytology, Muscle, Smooth metabolism, Receptors, Adrenergic drug effects, Receptors, Adrenergic physiology, Thionucleotides pharmacology, Calcium Channels drug effects, Isoproterenol pharmacology, Muscle, Smooth drug effects
- Abstract
1. The effects of isoprenaline (Iso) on Ca2+ channel current in enzymatically isolated single cells of the guinea-pig taenia caeci were examined using the standard whole-cell voltage-clamp method. 2. Iso potentiated the voltage-dependent Ca2+ current; the threshold and maximally effective concentration of Iso to increase Ca2+ current were 3-10 nM and 1-3 microM, respectively. The average increase in Ca2+ current produced by 3 microM Iso was 42 +/- 6% (mean +/- S.E.M.) and the response could be obtained repeatedly in the same cell. The concentration-response relationship could be fitted by a binding model with a Hill coefficient of 1 and a dissociation constant of 42 nM. 3. The effect of Iso on Ca2+ current was voltage dependent. Although potentiation of Ca2+ current by Iso was obvious between -30 and +10 mV, it was small or absent around +20 to +30 mV. Iso had little effect on the relationship between inactivation of the Ca2+ current and voltage obtained using a double-pulse protocol. 4. External application of forskolin, an adenylyl cyclase activator, or internal perfusion of cAMP or dibutyryl cAMP from the recording pipette, did not increase Ca2+ current and potentiation of Ca2+ current by Iso was observed repeatedly and was unchanged. 5. Internal perfusion of GTP gamma S or GDP beta S increased or did not affect the Ca2+ current and potentiation of Ca2+ current by Iso was unchanged and could be recorded repeatedly for about 20 min after rupture of the cell membrane. In addition, treatment of cells with the potent protein kinase C inhibitor, chelerythrine, had no effect on Ca2+ current or on potentiation of Ca2+ current by Iso. 6. These results suggest that the Ca2+ current in guinea-pig taenia caeci cells is potentiated by isoprenaline via mechanisms which do not involve either a cAMP pathway, a G-protein pathway or a protein kinase C pathway. The receptor involved appeared to be an atypical adrenoreceptor not blocked by either alpha- or beta-receptor blocking agents.
- Published
- 1993
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16. [Physiological functions and regulation of K+ and Cl- channels in single smooth muscle cells].
- Author
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Imaizumi Y, Muraki K, Henmi S, and Watanabe M
- Subjects
- Action Potentials, Adenosine Triphosphate metabolism, Animals, Calcium metabolism, Calcium Channels metabolism, Cell Separation, Cells, Cultured, Guinea Pigs, Membrane Potentials, Muscle, Smooth metabolism, Potassium Channels metabolism, Rabbits, Swine, Calcium Channels physiology, Muscle, Smooth cytology, Potassium Channels physiology
- Abstract
The major functional roles of K channels in smooth muscle cells are as follows: (i) Keeping resting membrane potential (RMP). (ii) Induction of hyperpolarization (HP) in response to bioactive substances. (iii) Facilitation of action potential repolarization (APR). (iv) Induction of action potential after-hyperpolarization (AH). (v) Facilitation of slow wave repolarization. (vi) Inhibition of depolarization and/or action potential. Major background K channels responsible for RMP have not been identified yet, whereas it is been postulated that several K channels including Ca-dependent K channels and ATP-dependent K channels may co-contribute in part to RMP. Further activation of these channels by bioactive substances results in hyperpolarization and muscle relaxation. APR and AH in several types of smooth muscles are due to activation of mainly large conductance Ca-dependent K channels (BK) and additionally delayed rectifier K channels. Moreover, another type of delayed rectifier K channels and early inactivating K channels may also contribute to some of the functional roles shown above. Although activation of Ca-dependent Cl channels in response to agonists depolarizes the cell membrane in several types of smooth muscle cells, a single channel current has not been identified. Ca-dependent K and Cl currents can be regulated by intracellular Ca store sites, which may be exhausted after a large release induced by inositol 1,4,5-trisphosphate or caffeine. The Ca-pump activity in the store sites may also regulate indirectly but strongly the activity of the channels and consequently membrane excitability.
- Published
- 1993
- Full Text
- View/download PDF
17. Cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum Ca(2+)-pump, reduces Ca(2+)-dependent K+ currents in guinea-pig smooth muscle cells.
- Author
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Suzuki M, Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Calcium pharmacology, Calcium-Transporting ATPases antagonists & inhibitors, Electric Conductivity, Electric Stimulation, Guinea Pigs, Ileum drug effects, Ileum metabolism, In Vitro Techniques, Muscle, Smooth cytology, Muscle, Smooth metabolism, Potassium metabolism, Sarcoplasmic Reticulum drug effects, Sarcoplasmic Reticulum enzymology, Urinary Bladder drug effects, Urinary Bladder metabolism, Calcium metabolism, Calcium-Transporting ATPases drug effects, Indoles pharmacology, Muscle, Smooth drug effects, Potassium Channels drug effects
- Abstract
1. Effects of cyclopiazonic acid (CPA), a specific inhibitor of the Ca(2+)-ATPase in sarcoplasmic reticulum (SR), on membrane ionic currents were examined in single smooth muscle cells freshly isolated from ileal longitudinal strips and urinary bladder of the guinea-pig. 2. Under whole-cell clamp, CPA (1-10 microM) reduced peak outward current elicited by depolarization in a concentration-dependent manner. The concentration of CPA required for 50% decrease in the peak outward current was approximately 3 microM in ileal cells under these conditions. The current reduced by CPA recovered by more than 70% after washout. 3. The transient outward current elicited by application of 5 mM caffeine at a holding potential of -50 mV in Ca2+ free solution was almost abolished, when the preceding Ca(2+)-loading of the cell in a solution containing 2.2 mM Ca2+ was performed in the presence of 3 microM CPA. 4. When the Ca(2+)-dependent K+ current (IK-Ca) and Ca2+ current (ICa) were inhibited by addition of Ca2+, the remaining delayed rectifier type K+ current was not affected by 10 microM CPA. When outward currents were blocked by replacement of K+ by Cs+ in the pipette solution, the remaining ICa was not affected by 10 microM CPA. 5. CPA (10 microM) did not affect the conductance of single maxi Ca(2+)-dependent K+ channels or the Cd(2+)-dependence of their open probability in both inside- and outside-out configurations. 6. These results indicate that IK-Ca is selectively and strongly suppressed by CPA.Its effects may be attributed to a decrease in Ca2"-uptake into SR, resulting in a decrease in Ca2"-induced Ca24 release which is triggered by Ca24 entering through voltage-dependent Ca24 channels and therefore less activation of these K channels.7. CPA may be extremely valuable pharmacological tool for investigating intracellular Ca24 mobilization and ionic currents regulated by intracellular Ca24.
- Published
- 1992
- Full Text
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18. Ca-dependent K channels in smooth muscle cells permeabilized by beta-escin recorded using the cell-attached patch-clamp technique.
- Author
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Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Acetylcholine pharmacology, Animals, Caffeine pharmacology, Electric Conductivity, Electrophysiology methods, Guinea Pigs, Inositol 1,4,5-Trisphosphate pharmacology, Male, Permeability, Signal Transduction, Calcium physiology, Escin pharmacology, Muscle, Smooth physiology, Potassium Channels physiology
- Abstract
Using the cell-attached patch-clamp technique, the activity of single, Ca-dependent K channels was recorded in single smooth muscle cells permeabilized by beta-escin. The conductance and the relationship between the open probability of the channels and pCa recorded in permeabilized cells were very similar to those obtained in excised inside-out patches. At pCa 7, application of 30 microM acetylcholine (ACh) or 0.1 microM substance P (SP) together with 1 mM guanosine 5'-trisphosphate to permeabilized cells elicited transient bursts of channel openings similar to those which occur in intact cells. Transient activation was also observed when 2-30 microM inositol trisphosphate (IP3) was applied to permeabilized cells. This single channel activity was inhibited by pretreatment with low-molecular-weight heparin at 50-100 micrograms/ml. Channel activity at pCa 7.0 was greatly enhanced by 200 microM cyclic adenosine monophosphate. These results provide direct evidence that single Ca-dependent K channel activity is regulated by the transmitters ACh and SP, as well as a second messenger, IP3, via the release of intracellular Ca from intracellular sites which are blocked by heparin. This novel approach is valuable in elucidating second messenger mechanisms involved in the regulation of single channel activity by transmitters and autocoids, since permeabilization by beta-escin preserves the entire system of receptor-operated signal transduction and allows intracellular application of second messengers at fixed concentrations.
- Published
- 1992
- Full Text
- View/download PDF
19. Effects of cyclopiazonic acid, a novel Ca(2+)-ATPase inhibitor, on contractile responses and an outward current in smooth muscle.
- Author
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Imaizumi Y, Suzuki M, Uyama Y, Muraki K, and Watanabe M
- Subjects
- Animals, Electrophysiology, Guinea Pigs, In Vitro Techniques, Male, Muscle Contraction drug effects, Calcium-Transporting ATPases antagonists & inhibitors, Indoles pharmacology, Muscle, Smooth drug effects
- Published
- 1992
20. Effects of norepinephrine (NE) on membrane currents recorded from single ureter smooth muscle cells of the guinea-pig.
- Author
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Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Guinea Pigs, In Vitro Techniques, Membranes drug effects, Membranes physiology, Muscle, Smooth cytology, Muscle, Smooth drug effects, Ureter cytology, Ureter drug effects, Muscle, Smooth physiology, Norepinephrine pharmacology
- Published
- 1992
21. Sodium currents in smooth muscle cells freshly isolated from stomach fundus of the rat and ureter of the guinea-pig.
- Author
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Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Gastric Fundus drug effects, Gastric Fundus physiology, Guinea Pigs, Manganese pharmacology, Membrane Potentials drug effects, Membrane Potentials physiology, Muscle, Smooth drug effects, Rats, Reaction Time, Sodium Channels drug effects, Tetrodotoxin pharmacology, Ureter physiology, Muscle, Smooth physiology, Sodium Channels physiology
- Abstract
1. Inward currents elicited by depolarization from holding potentials of -80 to -10 mV in single smooth muscle cells isolated from stomach fundus of the rat and ureter of the guinea-pig had two components. The initial fast component (Ifi) was activated and mostly inactivated within 1-2 and 10 ms, respectively, at 21 degrees C. The following sustained component (Isi) lasted over 50 and 500 ms in fundus and ureter cells, respectively. Ifi was blocked by tetrodotoxin but not affected by 0.5 microM-mu-conotoxin in both types of cells. Isi was abolished by the substitution of extracellular Ca2+ with Mn2+. 2. The sensitivity of Ifis to TTX was markedly different in fundus and ureter cells. The half-inhibition was obtained at 870 and 11 nM, respectively. The amplitude of Ifi was highly dependent on extracellular Na+ concentration in a solution containing 2.2 mM-Mn2+ and 0 mM-Ca2+ in both cells. It is concluded that Ifis in these cells are TTX-sensitive and mu-conotoxin-insensitive Na+ currents. 3. Some of the kinetics of INa measured at 10 degrees C were markedly different in fundus and ureter cells. The current-voltage relationships for Ifi in fundus and ureter cells had peaks at about -10 and 0 mV, respectively. The voltage dependence of the steady-state inactivation of Ifi was also significantly different in these cell types. The half-inactivation voltages were about -74 and -45 mV, respectively. The recovery time course from inactivation in fundus cells was about 10 times slower than that in ureter at -80 mV, where it was 25 ms. 4. The contribution of Ifi to the rising phase of an action potential was examined using TTX under current clamp mode at 21 degrees C. A fast notch-like potential elicited by a subthreshold stimulus for action potential generation was blocked by TTX in both types of cells. Action potentials elicited by a stimulus around threshold were occasionally suppressed by TTX, whereas an action potential was never observed when extracellular Ca2+ was replaced with Mn2+. 5. In conclusion, the existence of at least two types of Na+ channel currents, which were distinguished by their TTX sensitivity and kinetics, was strongly suggested in smooth muscle cells from the rat fundus and the guinea-pig ureter. INa in these cells may have a physiological role to accelerate the generation of an action potential by triggering a rapid activation of ICa, while not being essential for activation of action potentials.
- Published
- 1991
- Full Text
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22. Mechanisms of NE-induced reduction of Ca current in single smooth muscle cells from guinea pig vas deferens.
- Author
-
Imaizumi Y, Takeda M, Muraki K, and Watanabe M
- Subjects
- Animals, Barium pharmacology, Calcium pharmacology, Calcium Channels drug effects, Egtazic Acid pharmacology, Guanosine 5'-O-(3-Thiotriphosphate) pharmacology, Guinea Pigs, In Vitro Techniques, Kinetics, Male, Membrane Potentials drug effects, Muscle, Smooth drug effects, Phenylephrine pharmacology, Prazosin pharmacology, Vas Deferens drug effects, Calcium metabolism, Calcium Channels physiology, Muscle, Smooth physiology, Norepinephrine pharmacology, Vas Deferens physiology
- Abstract
Effects of norepinephrine (NE) on voltage-dependent Ca channel current (ICa) were examined applying whole cell patch-clamp technique to single smooth muscle cells freshly isolated from vas deferens of the guinea pig. K currents and contraction of the cell were abolished by Cs and EGTA in the pipette solution, respectively. The peak ICa and Ba current (IBa) elicited by depolarization from -60 mV in a solution containing 2.2 mM Ca or Ba were reduced by 10-60% in voltage- and dose-dependent manners by the application of NE or phenylephrine. This effect was greatly attenuated in the presence of prazosin. The decrease in IBa was always smaller than that in ICa at any potential. Even after simultaneous application of 5 mM caffeine and 10 microM NE to the cells in a Ba-containing solution, the second challenge with NE again reduced IBa in a similar manner. The decrease in IBa by 10 microM NE could not be explained well by a small shift (-5 mV) of the voltage dependence of the steady-state inactivation. The effect of NE on IBa was irreversibly enhanced by 0.1 mM guanosine 5'-O-(3-thiotriphosphate) and almost abolished by 1 mM guanosine 5'-O-(2-thiodiphosphate) added to the pipette solution but appeared not to be affected by the treatment with pertussis toxin. It can be concluded that, under these experimental conditions, the activation of alpha 1-adrenoceptor in vas deferens smooth muscle cells reduces Ca channel activity possibly via a mechanism involving GTP-binding protein in addition to Ca-mediated Ca channel inactivation mechanism.
- Published
- 1991
- Full Text
- View/download PDF
23. Characteristics of transient outward currents in single smooth muscle cells from the ureter of the guinea-pig.
- Author
-
Imaizumi Y, Muraki K, and Watanabe M
- Subjects
- Animals, Cadmium pharmacology, Calcium physiology, Cells, Cultured, Electrophysiology, Guinea Pigs, Muscle, Smooth drug effects, Potassium Channels physiology, Ureter drug effects, Muscle, Smooth physiology, Ureter physiology
- Abstract
1. Two kinds of transient outward currents were observed upon depolarization of single smooth muscle cells isolated from guinea-pig ureter. The major transient outward current was through Ca2(+)-activated K+ channels (IK(Ca) which had a large conductance (130 pS; 126 mM [K+]i/5.9 mM [K+]o). 2. The smaller transient outward current (ITO) was pharmacologically separated from other membrane currents in the presence of 1 mM-Cd2+ and 2 mM-tetraethylammonium(TEA+) and was selectively blocked by 3 mM-4-aminopyridine. It peaked (approximately 200 pA) within 10 ms upon depolarization from -80 to +20 mV and its half-inactivation time was approximately 50 ms at +20 mV. Half-maximum voltages (V 1/2) for activation and inactivation were about -8 and -50 mV, respectively, in the presence of 1 mM-Cd2+ and 2 mM-TEA+. The time course of recovery from inactivation of ITO was fitted with a single-exponential function (tau = 100 ms at -80 mV). A tenfold change of [K+]o resulted in a 53 mV change in the reversal potential of the tail of ITO. 3. Cadmium reduced peak ITO and shifted the voltage dependence of activation and inactivation in the positive direction in a concentration-dependent manner. The V 1/2 for inactivation in the absence of Cd2+ was estimated to be approximately -64 mV. 4. Single-channel outward currents which appeared only in the initial part of a depolarizing pulse from about -100 mV were recorded using the cell-attached patch clamp. The decay of the ensemble average of the current was similar to the macroscopic ITO under whole-cell clamp. When the holding potential was less negative, the opening probability of the channel greatly decreased. The channel conductance in normal extracellular medium was 14 pS. 5. In ureter cells ITO resembles A-type current. ITO does not contribute significantly to the repolarization of the action potential but it may regulate membrane excitability by opposing Ca2+ current activated around the threshold of the action potential.
- Published
- 1990
- Full Text
- View/download PDF
24. Effects of tetraethylammonium and 4-aminopyridine on outward currents and excitability in canine tracheal smooth muscle cells.
- Author
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Muraki K, Imaizumi Y, Kojima T, Kawai T, and Watanabe M
- Subjects
- Animals, Cadmium pharmacology, Dogs, Electrophysiology, In Vitro Techniques, Membrane Potentials drug effects, Muscle, Smooth cytology, Muscle, Smooth drug effects, Trachea drug effects, 4-Aminopyridine pharmacology, Ion Channels drug effects, Muscle, Smooth metabolism, Tetraethylammonium Compounds pharmacology
- Abstract
1. The effects of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on membrane currents and on single channel K currents in smooth muscle cells isolated from canine trachea were examined by use of tight seal whole cell- and patch-clamp techniques. 2. Depolarizing current applied through a recording pipette did not elicit an action potential under current clamp. A strong outward rectification was observed. 3. In most cells under voltage-clamp, only an outward current was observed upon depolarization from -60 mV when a pipette solution contained mainly KCl. The outward current consisted of three components; a large initial transient, a following sustained component and an additional component of irregular small transients on the sustained one. The two transient components were almost abolished when extracellular and pipette solutions contained 2.2 mM Cd2+ (0 mM Ca2+) and 10 mM EGTA, respectively. The sustained component was well maintained under these conditions. 4. TEA at low concentrations (less than 1 mM) effectively decreased the transient components and made the outward current smooth; it also suppressed the sustained component at higher concentrations. In outside-out patches, external 1 mM TEA reduced the single channel conductance of Ca-activated K channels by about 87% whereas 3 mM 4-AP did not. 4-AP at low concentrations (less than 3 mM) selectively reduced the sustained component of the outward current. 5. A Ca current recorded after the suppression of outward current by internal Cs+ had a peak of approximately 200 pA at +10 mV (holding potential: -60 mV). The half inactivation voltage in the steady-state was approximately -30 mV. 6. Simultaneous application of 1 mM TEA and 4-AP reduced the outward current and unmasked a Ca current. Under these conditions, an action potential with overshoot was easily elicited under current clamp. 7. It is concluded that the low excitability of canine tracheal smooth muscle cell upon depolarization is due to a large outward K current which consists of Ca-dependent and Ca-independent components. The peak amplitude of the Ca current is similar to that in highly excitable smooth muscle cells such as those of the ureter.
- Published
- 1990
- Full Text
- View/download PDF
25. [Effect of norepinephrine on the Ba current in isolated smooth muscle cells of the guinea pig vas deferens].
- Author
-
Takeda M, Muraki K, Imaizumi Y, and Watanabe M
- Subjects
- Animals, Guinea Pigs, In Vitro Techniques, Male, Vas Deferens metabolism, Barium metabolism, Ion Channels drug effects, Muscle, Smooth metabolism, Norepinephrine pharmacology
- Published
- 1989
26. A comparative study about voltage-dependent Ca currents in smooth muscle cells isolated from several tissues.
- Author
-
Watanabe M, Imaizumi Y, Muraki K, and Takeda M
- Subjects
- Animals, Cell Membrane physiology, Dogs, Electrochemistry, Guinea Pigs, Muscle, Smooth cytology, Organ Specificity, Rabbits, Calcium physiology, Muscle, Smooth physiology
- Published
- 1989
- Full Text
- View/download PDF
27. Ionic currents in single smooth muscle cells from the ureter of the guinea-pig.
- Author
-
Imaizumi Y, Muraki K, and Watanabe M
- Subjects
- 4-Aminopyridine pharmacology, Action Potentials drug effects, Animals, Cadmium pharmacology, Caffeine pharmacology, Calcium Channel Blockers pharmacology, Egtazic Acid pharmacology, Guinea Pigs, In Vitro Techniques, Lithium pharmacology, Tetraethylammonium, Tetraethylammonium Compounds pharmacology, Time Factors, Ureter physiology, Ion Channels physiology, Muscle, Smooth physiology
- Abstract
1. Ionic currents underlying the action potential were recorded from enzymatically isolated smooth muscle cells of guinea-pig ureter. 2. The action potential recorded from a single cell was similar to that from a multicellular preparation. It showed repetitive spikes on a plateau potential which followed the first spike. Treatment with 10 mM-tetraethylammonium (TEA) increased the amplitude and duration of the plateau phase and abolished the repetitive spikes. 3. Under voltage clamp mode, at least two (maybe three) kinds of outward currents were activated during depolarizing pulses. The main outward current was Ca2+-dependent K+ current (IK(Ca], which was mostly blocked in Ca2+-free solution, or by application of 1 mM-cadmium (Cd2+) or 2 mM-tetraethylammonium (TEA). IK(Ca) was greatly decreased by treatment with 5 mM-caffeine or an addition of 10 mM-EGTA in a pipette solution. 4. In the presence of 1 mM-Cd2+ and 2 mM-TEA, a small transient outward current remained. 4-Aminopyridine (1 mM) suppressed the transient outward current by about 40%. Time- and voltage-dependent delayed rectifier outward currents were small in ureter cells. An inwardly rectifying K+ current was not detected. 5. An application of 1 mM-Cd2+, 5 mM-cobalt (Co2+), 1 mM-lanthanum (La3+) or 0.1 microM-nifedipine completely blocked the action potential. Replacement of 80-90% of extracellular Na+ with Li+ or Tris almost abolished the plateau potential and repetitive spikes but did not change significantly the first spike. 6. In the presence of 30 mM-TEA, the inward current elicited by depolarization was monophasic and lasted for more than 1 s. Application of 1 mM-Cd2+, 1 mM-La3+, 0.1 microM-nifedipine, or 5 mM-Co2+ completely blocked inward current. The replacement (87%) of extracellular Na+ ions with Li+, Tris, sucrose or TEA speeded up the decay of inward current; the inward current decreased by 10-60% at the end of a 500 ms pulse. 7. Even in low-Na+ solution (120 mM-TEA), the inactivation of ICa had a quite slow component (tau = 1 s), in addition to another faster component (tau = 100 ms) at 0 mV. When short depolarizing clamp pulses (50 ms) were repetitively applied at short intervals (50 ms) and with interpulse voltage of -10 or -20 mV to mimic the repetitive spikes on the plateau of the action potential, the decline of peak Ca2+ current during the train of pulses was smaller than the decay of Ca2+ current during a long pulse.(ABSTRACT TRUNCATED AT 400 WORDS)
- Published
- 1989
- Full Text
- View/download PDF
28. Measurement and simulation of noninactivating Ca current in smooth muscle cells.
- Author
-
Imaizumi Y, Muraki K, Takeda M, and Watanabe M
- Subjects
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester pharmacology, Animals, Cadmium pharmacology, Calcium pharmacology, Calcium Channels drug effects, Cecum physiology, Electric Conductivity, Femoral Artery physiology, Guinea Pigs, Male, Membrane Potentials, Nifedipine pharmacology, Portal Vein physiology, Rabbits, Ureter physiology, Urinary Bladder physiology, Vas Deferens physiology, Calcium Channels physiology, Muscle, Smooth physiology
- Abstract
An attempt was made to obtain electrophysiological evidence for continuous influx of Ca ion through voltage-dependent Ca channel (VDCC) in smooth muscle during long depolarization, for example in high K solution. Noninactivated Ca current [ICa(ni)] remaining after the accomplishment of voltage-dependent inactivation by prolonged depolarization for approximately 1 min was detected by three means under whole cell voltage clamp in several types of smooth muscle cells. The measurement of ICa(ni) was performed by micropuff application of Cd2+ or Ca2+ in the presence or absence of 5 mM extracellular Ca, respectively, or jump of extracellular Ca concentration [( Ca]o). The current-voltage relationship of ICa(ni) evaluated by these means had a peak at approximately -10 mV. The peak amplitude ranged from 5 to 25 pA, depending on whether the cells were isolated from guinea pig urinary bladder, ureter, vas deferens, taenia caecum, or rabbit portal vein. The ICa(ni) may be large enough to explain sustained contraction in high K solution, at least in these smooth muscle tissues. A window current simulated from the steady-state activation and inactivation curves and the maximum conductance of Ca current (ICa) in these cells suggests a theoretical basis for the observed ICa(ni).
- Published
- 1989
- Full Text
- View/download PDF
29. Non-selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP
- Author
-
Beech, D J, Muraki, K, and Flemming, R
- Subjects
Molecular Sequence Data ,Animals ,Drosophila Proteins ,Humans ,Drosophila ,Muscle, Smooth ,Amino Acid Sequence ,Topical Review ,Ion Channels - Abstract
Throughout the body there are smooth muscle cells controlling a myriad of tubes and reservoirs. The cells show enormous diversity and complexity compounded by a plasticity that is critical in physiology and disease. Over the past quarter of a century we have seen that smooth muscle cells contain – as part of a gamut of ion-handling mechanisms – a family of cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G-protein-coupled receptor activation, membrane stretch, intracellular Ca2+, pH, phospholipid signals and other factors. Progress in understanding the channels has, however, been hampered by a paucity of specific pharmacological agents and difficulty in identifying the underlying genes. In this review we summarize current knowledge of these smooth muscle cationic channels and evaluate the hypothesis that the underlying genes are homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2, and more are likely to be added soon. Some of these TRP proteins respond to a multiplicity of activation signals – promiscuity of gating that could enable a variety of context-dependent functions. We would seem to be witnessing the first phase of the molecular delineation of these cationic channels, something that should prove a leap forward for strategies aimed at developing new selective pharmacological agents and understanding the activation mechanisms and functions of these channels in physiological systems.
- Published
- 2004
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