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Pulmonary vessels play a pivotal role in oxygen circulation. We previously demonstrated that pimaric acid (PiMA) activated large-conductance Ca2+-activated K+ (BKCa) channels and inhibited voltage-dependent Ca2+ channels (VDCCs). In the present study, PiMA attenuated vasoconstriction induced by high K+ or endothelin-1 in rat pulmonary arterial smooth muscles (PASMs). PiMA also reduced high K+-induced cytosolic [Ca2+] increase in PASM cells. PiMA increased BKCa currents and decreased VDCC currents. BKCa channels and VDCCs were formed by the α/β1 and α1C/α1D/β2/β3 subunits, respectively. These results indicate that PiMA induces vasorelaxation through the dual effects of BKCa channel activation and VDCC inhibition in PASMs.

Melatonin is synthesized in and secreted from the pineal glands and regulates circadian rhythms. Although melatonin has been reported to modulate the activity of ion channels in several tissues, its effects on pineal ion channels remain unclear. In the present study, the effects of melatonin on voltage-gated K+ (KV) channels, which play a role in regulating the resting membrane potential, were examined in rat pinealocytes. The application of melatonin reduced pineal KV currents in a concentration-dependent manner (IC50 = 309 µM). An expression analysis revealed that KV4.2 channels were highly expressed in rat pineal glands. Melatonin-sensitive currents were abolished by the small interfering RNA knockdown of KV4.2 channels in rat pinealocytes. In human embryonic kidney 293 (HEK293) cells expressing KV4.2 channels, melatonin decreased outward currents (IC50 = 479 µM). Inhibitory effects were mediated by a shift in the voltage dependence of steady-state inactivation in a hyperpolarizing direction. This inhibition was observed even in the presence of 100 nM luzindole, an antagonist of melatonin receptors. Melatonin also blocked the activity of KV4.3, KV1.1, and KV1.5 channels in reconstituted HEK293 cells. The application of 1 mM melatonin caused membrane depolarization in rat pinealocytes. Furthermore, KV4.2 channel inhibition by 5 mM 4-aminopyridine attenuated melatonin secretion induced by 1 µM noradrenaline in rat pineal glands. These results strongly suggest that melatonin directly inhibited KV4.2 channels and caused membrane depolarization in pinealocytes, resulting in a decrease in melatonin secretion through parasympathetic signaling pathway. This mechanism may function as a negative-feedback mechanism of melatonin secretion in pineal glands. [ABSTRACT FROM AUTHOR]

The blood–brain barrier (BBB) is mainly formed by brain capillary endothelial cells (BCECs) and is exposed to hypoxic environments under pathological conditions. The effects of hypoxia on the expression and activity of Ca2+-activated Cl− (ClCa) channels, TMEM16A, were examined in bovine brain endothelial t-BBEC117 cells and mouse BCECs. The expression of TMEM16A was upregulated by hypoxia. Whole-cell ClCa currents increased under hypoxia. Hypoxia also increased cell proliferation and trans-endothelial permeability, which were attenuated by ClCa channel blockers or TMEM16A siRNA. These findings are useful for elucidating the pathological role of TMEM16A ClCa channels in the BBB during cerebral ischemia.

Portal hypertension is defined as an increased pressure in the portal venous system and occurs as a major complication in chronic liver diseases. The pathological mechanism underlying the pathogenesis and development of portal hypertension has been extensively investigated. Vascular tone of portal vein smooth muscles (PVSMs) is regulated by the activities of several ion channels, including Ca2+-activated Cl− (ClCa) channels. TMEM16A is mainly responsible for ClCa channel conductance in vascular smooth muscle cells, including portal vein smooth muscle cells (PVSMCs). In the present study, the functional roles of TMEM16A channels were examined using two experimental portal hypertensive models, bile duct ligation (BDL) mice with cirrhotic portal hypertension and partial portal vein ligation (PPVL) mice with non-cirrhotic portal hypertension. Expression analyses revealed that the expression of TMEM16A was downregulated in BDL-PVSMs, but not in PPVL-PVSMs. Whole-cell ClCa currents were smaller in BDL-PVSMCs than in sham- and PPVL-PVSMCs. The amplitude of spontaneous contractions was smaller and the frequency was higher in BDL-PVSMs than in sham- and PPVL-PVSMs. Spontaneous contractions sensitive to a specific inhibitor of TMEM16A channels, T16Ainh-A01, were reduced in BDL-PVSMs. Furthermore, in normal PVSMs, the downregulation of TMEM16A expression was mimicked by the exposure to angiotensin II, but not to bilirubin. This study suggests that the activity of ClCa channels is attenuated by the downregulation of TMEM16A expression in PVSMCs associated with cirrhotic portal hypertension, which is partly mediated by increased angiotensin II in cirrhosis.

The ionotropic purinergic P2X7 receptor responds to extracellular ATP and can trigger proinflammatory immune signaling in macrophages. Caveolin-1 (Cav-1) is known to modulate functions of macrophages and innate immunity. However, it is unknown how Cav-1 modulates P2X7 receptor activity in macrophages. We herein examined P2X7 receptor activity and macrophage functions using bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cav-1 knockout (KO) mice. ATP (1 mM) application caused biphasic increase in cytosolic [Ca2+] and sustained decrease in cytosolic [K+]. A specific P2X7 receptor blocker, A-740003, inhibited the maintained cytosolic [Ca2+] increase and cytosolic [K+] decrease. Total internal reflection fluorescent imaging and proximity ligation assays revealed a novel molecular complex formation between P2X7 receptors and Cav-1 in WT BMDMs that were stimulated with lipopolysaccharides. This molecular coupling was increased by ATP application. Specifically, the ATP-induced Ca2+ influx and K+ efflux through P2X7 receptors were increased in Cav-1 KO BMDMs, even though the total and surface protein levels of P2X7 receptors in WT and Cav-1 KO BMDMs were unchanged. Cell-impermeable dye (TO-PRO3) uptake analysis revealed that macropore formation of P2X7 receptors was enhanced in Cav-1 KO BMDMs. Cav-1 KO BMDMs increased ATP-induced IL-1β secretion, reactive oxygen species production, Gasdermin D (GSDMD) cleavage, and lactate dehydrogenase release indicating pyroptosis. A-740003 completely prevented ATP-induced pyroptosis. In combination, these datasets show that Cav-1 has a negative effect on P2X7 receptor activity in BMDMs and that Cav-1 in macrophages may contribute to finely tuned immune responses by preventing excessive IL-1β secretion and pyroptosis. NEW & NOTEWORTHY: In bone marrow-derived macrophages, Cav-1 suppresses the macropore formation of P2X7 receptors through their direct or indirect interactions, resulting in reduced membrane permeability of cations (Ca2+ and K+) and large cell-impermeable dye (TO-PRO3) induced by ATP. Cav-1 also inhibits ATP-induced IL-1β secretion, ROS production, GSDMD cleavage, and pyroptosis. Cav-1 contributes to the maintenance of proper immune responses by finely tuning IL-1β secretion and cell death in macrophages. [ABSTRACT FROM AUTHOR]

Voltage-gated K+ (KV) channels, which control firing and shape of action potentials in excitable cells, are supposed to be potential therapeutic targets in many types of diseases. Pimaric acid (PiMA) is a unique opener of large conductance Ca2+-activated K+ channel. Here, we report that PiMA modulates recombinant rodent KV channel activity. The enhancement was significant at low potentials (

An improved understanding of fundamental physiological principles and progressive pathophysiological processes in human articular joints (e.g., shoulders, knees, elbows) requires detailed investigations of two principal cell types: synovial fibroblasts and chondrocytes. Our studies, done in the past 8–10 years, have used electrophysiological, Ca2+ imaging, single molecule monitoring, immunocytochemical, and molecular methods to investigate regulation of the resting membrane potential (ER) and intracellular Ca2+ levels in human chondrocytes maintained in 2-D culture. Insights from these published papers are as follows: (1) Chondrocyte preparations express a number of different ion channels that can regulate their ER. (2) Understanding the basis for ER requires knowledge of (a) the presence or absence of ligand (ATP/histamine) stimulation and (b) the extraordinary ionic composition and ionic strength of synovial fluid. (3) In our chondrocyte preparations, at least two types of Ca2+-activated K+ channels are expressed and can significantly hyperpolarize ER. (4) Accounting for changes in ER can provide insights into the functional roles of the ligand-dependent Ca2+ influx through store-operated Ca2+ channels. Some of the findings are illustrated in this review. Our summary diagram suggests that, in chondrocytes, the K+ and Ca2+ channels are linked in a positive feedback loop that can augment Ca2+ influx and therefore regulate lubricant and cytokine secretion and gene transcription.

Ion channels play pivotal roles in a wide variety of cellular functions; therefore, their physiological characteristics, pharmacological responses, and molecular structures have been extensively investigated. However, the mobility of an ion channel itself in the cell membrane has not been examined in as much detail. A total internal reflection fluorescence (TIRF) microscope allows fluorophores to be imaged in a restricted region within an evanescent field of less than 200 nm from the interface of the coverslip and plasma membrane in living cells. Thus the TIRF microscope is useful for selectively visualizing the plasmalemmal surface and subplasmalemmal zone. In this review, we focused on a single-molecule analysis of the dynamic movement of ion channels in the plasma membrane using TIRF microscopy. We also described two single-molecule imaging techniques under TIRF microscopy: fluorescence resonance energy transfer (FRET) for the identification of molecules that interact with ion channels, and subunit counting for the determination of subunit stoichiometry in a functional channel. TIRF imaging can also be used to analyze spatiotemporal Ca2+ events in the subplasmalemma. Single-molecule analyses of ion channels and localized Ca2+ signals based on TIRF imaging provide beneficial pharmacological and physiological information concerning the functions of ion channels.

Two-pore-domain K+ (K2P) channels sense a wide variety of stimuli such as mechanical stress, inhalational anesthetics, and changes in extracellular pH or temperature. The K2P channel activity forms a background K+ current and, thereby, contributes to resting membrane potentials. Six subfamilies including fifteen subtypes of K2P channels have been identified. Each K2P channel molecule with two pores consists of a homodimer of each subtype. In addition, a few heterodimers mainly within the same subfamilies have been found recently. In the present study, the possibility of heterodimerization between TASK1 (TWIK-Related Acid-Sensitive K+ channel) and TALK2 (TWIK-Related Alkaline pH-Activated K+ channel) was examined. These channels belong to separate subfamilies and show extremely different channel properties. Surprisingly, single molecular imaging analyses in this study using a total internal reflection microscope suggested the heterodimerization of TASK1 and TALK2 in a pancreatic cell line, QGP-1. This heterodimer was also detected using a bimolecular fluorescence complementation assay in a HEK293 heterologous expression system. Fluorescence resonance energy transfer analyses showed that the affinity between TASK1 and TALK2 appeared to be close to those of homodimers. Whole-cell patch-clamp recordings revealed that TASK1 currents in HEK293 cells were significantly attenuated by co-expression of a dominant-negative form of TALK2 in comparison with that of wild-type TALK2. The sensitivities of TASK1-TALK2 tandem constructs to extracellular pH and halothane were characterized as a unique hybrid of TASK1 and TALK2. These results suggested that heterodimerization of TASK1 and TALK2 provides cells with the ability to make multiple responses to a variety of physiological and pharmacological stimuli.

Abstract.: TMEM16A is a major component of Ca2+-activated Cl− channel (CaCC) conductance in murine portal vein smooth muscle cells (mPVSMCs). Here, the regulation of CaCC activity by the actin cytoskeleton was examined in mPVSMCs. Actin disruption by cytochalasin D did not affect the current density, but increased the deactivation time constant in mPVSMCs. The elongated deactivation was recovered by jasplakinolide. When murine TMEM16A was transfected into HEK293 cells that have a poorly developed actin cytoskeleton, electrophysiological properties of CaCC currents were not changed by cytochalasin D. In conclusion, the CaCC activity in mPVSMCs is modified by the interaction of TMEM16A with abundant actin cytoskeleton. Keywords:: TMEM16A, actin cytoskeleton, portal vein

Abstract.: Upregulation of the Kir2.1 channel during endoplasmic reticulum (ER) stress in t-BBEC117, an immortalized bovine brain endothelial cell line, caused a sustained increase in intracellular Ca2+ concentration ([Ca2+]i) and a facilitation of cell death. Expressions of Ca2+ influx channels (TRPC, Orai1, STIM1) were unchanged by ER stress. The ER stress–induced [Ca2+]i increase was mainly attributed to the deeper resting membrane potential due to Kir2.1 upregulation. ER stress arrested at the G2/M phase and it was attenuated by an inhibitor of Kir2.1. These results indicate that Kir2.1 upregulation by ER stress facilitates cell death via regulation of cell cycle progression in t-BBEC117. Keywords:: brain capillary endothelial cell, store operated calcium entry, endoplasmic reticulum stress

To develop a simple screening system for blockers of voltage-gated Kv1.3 and Kv1.5 channels, new cell lines co-expressing mutated Nav1.5 (IFM/Q3), Kir2.1 (Kir), and Kv1.3 or Kv1.5 were introduced as IFM/Q3+Kir+Kv1.3 and IFM/Q3+Kir+Kv1.5, respectively. Electrical stimulation (ES) of a cell line, IFM/Q3+Kir, induced prolonged action potentials due to the slow inactivation of IFM/Q3 and subsequent cell death. Additional co-expression of Kv1.3 or Kv1.5 to IFM/Q3+Kir shortened the evoked action potentials and prevented cell death. In the presence of margatoxin, a selective Kv1.3-blocker, ES induced cell death in IFM/Q3+Kir+Kv1.3, but not in IFM/Q3+Kir+Kv1.5. In the presence of 4-aminopyridine, a non-selective Kv-channel blocker, ES application elicited cell death in both cell lines. The IC50s of acacetin, a Kv1.5-blocker, was 10.2 μM in IFM/Q3+Kir+Kv1.3 and almost identical to that in IFM/Q3+Kir+Kv1.5 (7.6 μM). The IC50s of citalopram, a 5-HT uptake-inhibitor, were 1.8 μM in IFM/Q3+Kir+Kv1.3 and 1.5 μM in IFM/Q3+Kir+Kv1.5, respectively. These IC50s were comparable to those determined electrophysiologically. In conclusion, acacetin and citalopram block both Kv1.3 and Kv1.5 without selectivity. The Kv1.3 or Kv1.5 channel inhibition assay using these new cell lines may be applicable to high–throughput screening because of its simplicity, accuracy, and high cost-performance. Keywords:: Kv1.3, Kv1.5, high-throughput screening, acacetin, citalopram

The rise of Ca2+ concentration ([Ca2+] i ) by reducing external Na+ in urinary bladder smooth muscle cells (UBSMCs) from transgenic mice overexpressing Na+/Ca2+ exchanger type-1.3 (NCX1.3tg/tg) was about 4 times as large as that in the wild-type (WT). NCX1 protein expression in UB increased about 4-fold in NCX1.3tg/tg. The Ca2+ release by caffeine in UBSMCs was comparable between NCX1.3tg/tg and WT, but [Ca2+]i decay was faster in NCX1.3tg/tg. Contractions induced by acetylcholine, 60 mM K+, or electrical stimulation were significantly smaller in UB segments of NCX1.3tg/tg. NCX worked in Ca2+-extrusion mode during these contractions in UBSMCs of both WT and NCX1.3tg/tg. Keywords:: Na+-Ca2+ exchanger, urinary bladder smooth muscle, transgenic mouse

Abstract.: The contribution of Cl− conductance relative to that of K+ in the regulation of membrane potential was examined using OUMS-27 cells, a model cell-line of human chondrocytes. Application of 100 μM niflumic acid (NFA) and other anion-channel blockers induced significant membrane hyperpolarization. The NFA-sensitive membrane current under voltage-clamp was predominantly Cl− current. Application of NFA induced small but significant increase in intracellular Ca2+ concentration ([Ca2+]i) and markedly enhanced the late component of [Ca2+]i rise induced by 1 μM histamine. In conclusion, Cl− conductance substantially contributes to the regulation of resting membrane potential and [Ca2+]i in OUMS-27 cells. Keywords:: chondrocyte, chloride channel, niflumic acid

Large-conductance Ca2+-activated K+ (BK) channel regulates action potential firing in pancreatic β-cells. We cloned novel spliced variants of the BK-channel β2-subunit (BKβ2b), which consisted of 36 amino acids including the N-terminal in the original human BKβ2 (BKβ2a), from human and rodent pancreas. Real-time PCR analysis showed the abundant expression of BKβ2b transcripts in human and rodent pancreas and also in the RINm5f insulinoma cell line. In addition, up-regulation of both BK-channel α-subunit (BKα) and BKβ2b transcripts was observed in pancreas tissues from diabetes mellitus patients. In HEK293 cells co-expressing BKα and BKβ2b, the inactivation of BK-channel currents, which is typical for BKα + BKβ2a, was not observed, and electrophysiological and pharmacological properties of BKα + BKβ2b were almost identical to those of BKα alone. In HEK293 cells stably expressing BKα, the transient co-expression of yellow fluorescence protein (YFP)-tagged BKβ2a proteins resulted in their distribution along the cell membrane. In contrast, the co-expression of YFP-tagged BKβ2b with BKα showed diffusely distributed fluorescence signals throughout the cell body. Taken together, the predominant splicing of BKβ2b versus that of BKβ2a presumably enhances the contribution of BK channels to membrane potential and may possibly be a factor modulating insulin secretion in a suppressive manner in pancreatic β-cells. Keywords:: Ca2+-activated K+ channel, β2-subunit, spliced variant, pancreatic islet β-cell, diabetes mellitus

Abstract.: Ca2+ release from intracellular store sites via the ryanodine receptor (RyR) and hormonal regulation by flutamide, an androgen-receptor (AR) antagonist, on it were examined in vas deferens (VD) smooth muscle cells (SMCs). VD and VDSMCs were obtained from two groups of male rats that were treated p.o. with 100 mg/kg flutamide (Flu) or vehicle (Vehicle). Both spontaneous and caffeine-induced Ca2+ releases were markedly smaller in single VDSMCs from Flu than in those from Vehicle. Interestingly, [Ca2+]i rise by 100 μM norepinephrine in VDSMCs from Flu was larger than that in those from Vehicle. The contractions induced by direct electrical stimulation in tissue preparations from Flu showed lower susceptibility to 30 μM ryanodine than those from Vehicle. Real-time PCR analyses revealed that the transcripts of ryanodine receptor (RyR) type 2 and type 3 (RyR2 and RyR3) were expressed in VD and markedly reduced in Flu. The protein expression of total RyR was significantly reduced by flutamide treatment, but that of inositol 1,4,5-trisphosphate receptor (IP3R) was not affected. It can be strongly suggested that long term block of AR by flutamide reduced the expression of RyR and its contribution to the contraction, but not those of IP3R in VDSMCs. Keywords:: ryanodine receptor, Ca2+ release, flutamide, vas deferens, smooth muscle

K+ channels are key molecules in the progression of several cancer types and considered to be potential targets for cancer therapy. We examined the gene expressions of voltage-gated (Kv), Ca2+-activated (KCa), and two-pore domain (K2P) K+-channel subtypes in needle-biopsy samples of human prostate cancer (PCa) by real-time PCR and compared them with those in PCa epithelial cell lines. The expression of Kv1.3, KCa1.1, KCa3.1, and K2P1 markedly increased in the PCa group with Gleason score of 5 – 6 (GS5–6) but significantly decreased in the GS8–9 group. This malignancy grade–dependent K+-channel expression pattern may provide a convenient marker to understand PCa progression level. Keywords:: prostate cancer, K+ channel, tumor marker

We characterized the effects of sphingosine-1-phosphate (S1P) on rat aortic myocytes with or without culture. Application of S1P induced a small Ca2+ response in 40% freshly dispersed aortic myocytes, whereas S1P caused a larger Ca2+ response in 90% myocytes cultured for 72 h. Concentration–response relationships of S1P in cultured myocytes were significantly different from that in non-cultured myocytes. Analysis of the expression of S1P-receptor mRNA transcripts revealed that S1P-receptor type 3 (S1P3) was significantly increased when myocytes were cultured for 24 h. Neither the removal of serum from culture medium nor pretreatment with pharmacological agents, such as ERK, Rho, and PI3 kinase inhibitors, affected the progression of the S1P-induced Ca2+ response during culture. The sustained component of the Ca2+ response to S1P was sensitive to the removal of external Ca2+ and was effectively inhibited by inorganic Ca2+-channel blockers such as Gd3+, Cd2+, and Ni2+. However, application of S1P did not induce any contraction in organ-cultured as well as the intact aorta muscle strip. Aortic myocytes freshly dispersed from the organ-cultured muscle were also ineffective against S1P. Taken together, cell-culture changes the S1P3-mediated Ca2+ response to S1P in rat aortic myocytes. Keywords:: sphingosine-1-phosphate (S1P), S1P3 receptor, rat aorta, cell culture

In this study, we provide evidence of critical changes in the expression of non-selective cation currents (NSCC) during culture in rat aortic myocytes. A selective TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4αPDD), had little effect on membrane currents and intracellular Ca2+ (Ca2+i) in freshly isolated cells from the aorta. In contrast, in cultured aortic myocytes with and without serum, 4αPDD at a concentration range between 0.3 and 3 μM effectively elevated Ca2+i, which was abolished in the absence of external Ca2+. Application of 4αPDD to cultured aortic myocytes also activated NSCC, which had a reversal potential of +3 mV. Both of these signals were blocked by ruthenium red (RuR), an effective blocker of TRPVs. Although the expression of TRPV4 mRNA transcript was found in cultured as well as non-cultured aortic myocytes, significant immunoreactivity to TRPV4 protein was only detected in cultured rat aortic myocytes. Moreover, cultured human pulmonary arterial smooth muscle cells (hPASM) had a substantial response to 4αPDD, which was susceptible to the removal of external Ca2+ and application of RuR. These results provide a strong basis for our proposal that endogenous TRPV4 functions as an important regulator of Ca2+i in vascular myocytes under some physiological and pathophysiological conditions. Keywords:: TRPV4, 4α-phorbol 12,13-didecanoate, cell-culture

It has been suggested that a new type of large-conductance Ca2+-activated K+ (BK) channel is distributed in the inner mitochondrial membrane (mitoKCa channel) and that its opening may attenuate ischemic cardiac injury. We examined effects of 12,14-dichlorodehydroabietic acid (diCl-DHAA), a novel BK-channel opener, on rat cardiac myocytes and mitochondria. Application of diCl-DHAA concentration-dependently reduced Ca2+ overload in isolated mitochondria, activated mitoKCa channels in inside-out patches of mitochondrial membrane, facilitated flavoprotein-oxidization in myocytes, and increased cellular viability under simulated ischemia. In conclusion, diCl-DHAA directly opens mitoKCa channels, prevents Ca2+ influx into matrix, and reduces ischemic injury in cardiac myocytes. Keywords:: mitochondria, large-conductance Ca2+-activated K+ (BK) channel, cardiac ischemia

ATP-receptor (P2Y) stimulation induced sustained Ca2+-entry, which was essential for the enhanced cell-proliferation in t-BBEC117, an immortalized cell-line derived from bovine brain endothelial cells. Application of Ca2+ following store-depletion with thapsigargin in Ca2+-free solution induced Ca2+-entry through store-operated channels (SOCs). Ca2+-entry induced by ATP or 1-oleoyl-2-acetyl-sn-glycerol (OAG) together with Ca2+ was significantly larger than that by Ca2+ alone, suggesting the involvement of receptor-operated channels (ROCs) in the Ca2+-entry. Results obtained using pharmacological tools suggest that the contribution of Ca2+ sources to ATP-induced [Ca2+]i rise in t-BBEC117 is estimated as approximately 2:1:2 for Ca2+-release and Ca2+-entry though SOCs and ROCs, respectively. Keywords:: brain capillary endothelial cell, store-operated channel, receptor-operated channel

Small-conductance Ca2+-activated K+ (SK2) channel plays an important role in the activation of Jurkat T-lymphocytes by maintaining electrical gradients for the sustained Ca2+ influx. Apamin-sensitive K+ current was significantly decreased with cell-cycle progression from G0/G1 into G2/M phases, and protein expression of SK2 channels showed parallel downregulation, with its highest expression at early G0/G1 phase. In the G0/G1 phase, the apamin-sensitive component of thapsigargin-induced Ca2+ influx was significantly larger than that in the G2/M phase. These observations suggest that SK2-channel activation may largely contribute to the sustained Ca2+ influx in the G0/G1 phase in comparison of that in the G2/M phase in Jurkat T-lymphocytes. Keywords:: Jurkat T-lymphocyte, small-conductance Ca2+-activated K+ (SK2) channel, cell-cycle progression

We examined the effects of methyl-β-cyclodextrin (MβCD) on Ca2+-induced Ca2+ release (CICR) in smooth muscle cells (SMCs) of mouse urinary bladder (UB). Short depolarization of UBSMCs under voltage-clamp elicited several local Ca2+ transients (Ca2+ hot spots) via CICR within 20 ms in discrete sub-sarcolemmal areas. Then, the Ca2+ wave spread to whole areas. The pretreatment with 10 mM MβCD significantly attenuated Ca2+ hot spots in UBSMCs and reduced contraction by single direct electrical pulse stimulation in UBSM strips. MβCD may prevent CICR by attenuating the coupling between voltage-dependent Ca2+ channels and ryanodine receptors in Ca2+ hot spot areas. Keywords:: methyl-β-cyclodextrin, Ca2+-induced Ca2+ release, smooth muscle

Abstract.: We examined effects of small and intermediate conductance Ca2+-activated K+ (SK and IK) channel openers, DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) and NS309 (3-oxime-6,7-dichloro-1H-indole-2,3-dione), on L-type Ca2+ channel current (ICa) that was measured in smooth muscle cells isolated from mouse urinary bladder under whole cell voltage-clamp. The ICa was concentration-dependently inhibited by DCEBIO and NS309; half inhibition was obtained at 71.6 and 10.6 µM, respectively. The specificity of NS309 to the IK channel over the Ca2+ channel appears to be high and higher than that of DCEBIO. DCEBIO and even NS309 may, however, substantially block Ca2+ channels when used as SK channel openers. Keywords:: voltage-dependent Ca2+ channel, DCEBIO, NS309

ABSTRACT: Effects of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N′-cyano-3-pyridinecarboxamidine), a novel K+ channel opener, on ionic currents were examined in rabbit femoral arterial myocytes (RFAMs). Under whole-cell clamp conditions where cells were superfused with 5.9 mM K+ bathing solution, KRN4884 elicited an outward current at -30 mV. KRN4884-induced current had a reversal potential of -78 mV and was abolished by application of glibenclamide (glib). KRN4884 was approximately 43 times more potent than levcromakalim in activating an ATP-sensitive K+ current (IK-ATP). On the other hand, KRN4884 affected neither voltage-dependent Ca2+ nor delayed rectifier K+ channel currents. In the inside-out patch clamp configuration where cells were superfused with the symmetrical 140 mM K+ solution, KRN4884 activated 47 pS K+ channels in the presence of adenosine diphosphate. Similar 47 pS K+ channels, which were reversibly inhibited by glib, were recorded under outside-out patch conditions. Using RT-PCR analysis, we found that inward rectifier K channel 6.1 (Kir6.1) and sulfonylurea 2B (SUR2B) transcripts were predominantly expressed in rabbit femoral artery. These results indicate that KRN4884 potently activates IK-ATP in RFAMs. The KRN4884-sensitive 47 pS K+ channel activity underlying IK-ATP is a vascular type KATP channel consisting of Kir6.1 and SUR2B and has similar characteristics to those of ATP-sensitive K+ channels activated by K+ channel openers in other types of smooth muscles.

Palmitoyl-L-carnitine (palcar), which accumulates in ischemic heart, affects cellular functions of vascular endothelium in the ischemic area. The aim of this study was to examine the effects of palcar on intracellular Ca2+ concentration ([Ca2+]i) in vascular endothelial cells in comparison with those of sphingosine-1-phosphate (S1P) and to investigate the underlying mechanisms. Application of palcar at a concentration range between 0.3 and 3 μM elevated [Ca2+]i in huvecs, and its potency was about 30 times lower than that of S1P. When human umbilical vein endothelial cells (huvecs) were treated with 100 ng/ml pertussis toxin (PTX) for 15 h, they failed to respond to palcar or S1P, but did respond to 3 μM histamine (His), suggesting that the response induced by palcar as well as S1P is mediated by a PTX-sensitive GTP binding protein, Gi. Although the sensitivity to palcar and S1P varied widely among huvecs from individuals, response to 3 μM palcar in each huvec clearly paralleled that to 0.3 μM S1P (r = 0.79, P

Mitochondria buffer cytosolic Ca2+ increases following Ca2+ influx from extracellular spaces, and Ca2+ release from intracellular Ca2+ store sites under physiological circumstances. Therefore, close contact of mitochondria with the sarcoplasmic reticulum (SR) is required for maintaining Ca2+ homeostasis. Mitofusin 2 (Mfn2) localizes in both mitochondrial and SR membranes and is hypothesized to optimize the distance and Ca2+ transfer between these organelles. However, the physiological significance of Mfn2 in vascular smooth muscle cells (VSMCs) is poorly understood. In the present study, the role of Mfn2 in the physical and functional couplings between SR and mitochondria was examined in rat aortic smooth muscle cells (rASMCs) by confocal and electron microscope imaging. When Mfn2 was knocked down using siRNA in rASMCs, the mean distance between these organelles was extended from 16.2 to 21.6 nm. The increase in the cytosolic Ca2+ concentration ([Ca2+]cyt) induced by 100 nM arginine vasopressin (AVP) was not affected by Mfn2 siRNA knockdown, whereas cytosolic Ca2+ removal was slower after Mfn2 knockdown. Following the AVP-induced [Ca2+]cyt increase, mitochondrial Ca2+ uptake and Ca2+ refill into the SR were attenuated by Mfn2 knockdown. In addition, Mfn2-knockdown cells exhibited a loss of mitochondrial membrane potential (DWmito) and lower ATP levels in mitochondria. Moreover, Mfn2 knockdown inhibited cell proliferation. In contrast, Mfn2 overexpression increased Δmito and cell growth. This study strongly suggests that Mfn2 is responsible for SR-mitochondria Ca2+ signaling by tethering mitochondria to SR, thereby regulating ATP production and proliferation of VSMCs. [ABSTRACT FROM AUTHOR]