Search

The effects of quercetin, a natural polyphenolic compound, on voltage-dependent L-type Ca(2+) current (I(Ca,L)) in rat pituitary GH(3) cells were investigated with the aid of the whole-cell voltage-camp technique. Quercetin (0.5-200 microM) stimulated I(Ca,L) in a concentration-dependent manner. The current-voltage (I-V) relationship of I(Ca,L) was slightly shifted to more negative potentials in the presence of quercetin. The EC(50) value of the quercetin-induced stimulation of I(Ca,L) was about 7 microM. The presence of quercetin (5 microM) shifted the steady state inactivation curve of I(Ca,L) to a more negative potential by approximately -10 mV. Although quercetin might increase intracellular cyclic AMP, sp-cAMPS did not affect I(Ca,L). In addition, neither flavone nor wortmannin had any effect on the amplitude of I(Ca,L), while epicatechin and genistein slightly suppressed it. Quercetin (50 microM) decreased the amplitude of tetrodotoxin-sensitive Na(+) current in GH(3) cells. Under current-clamp configuration, quercetin could increase the firing frequency of actions potentials. Conversely, in NG108-15 neuronal cells, quercetin suppressed the amplitude of I(Ca,L). The quercetin-induced inhibition of I(Ca,L) was abolished in NG108-15 cells preincubated with t-butyl hydroperoxide (1 mM). Quercetin-mediated stimulation of I(Ca,L) in GH(3) cells was presumably not associated with the level of intracellular cyclic AMP, or with the activity of tyrosine or phosphoinositide 3-kinases. Therefore, the effects of quercetin on ion currents may, at least in part, contribute to the underlying mechanisms through which it affects neuronal or neuroendocrine function., (Copyright 2003 Wiley-Liss, Inc.)

Quinones have been shown to possess antineoplastic activity; however, their effects on ionic currents remain unclear. The effects of 2-mercaptophenyl-1,4-naphthoquinone (2-MPNQ), menadione (MD) and 1,4-naphthoquinone (1,4 NQ) on cell proliferation and ionic currents in pituitary GH3 lactotrophs were investigated in this study. 2-MPNQ was more potent than menadione or 1,4-naphthoquinone in inhibiting the growth of GH3 cells. 2-MPNQ decreased cell proliferation in a concentration-dependent manner with an IC50 value of 3 microM. In whole-cell recording experiments, 2-MPNQ reversibly caused an inhibition of Ca2+-activated K+ current (I(K(Ca)) in a concentration-dependent manner. The IC50 value for 2-MPNQ-induced inhibition of I(K(Ca)) was 7 microM. In the inside-out configuration of single channel recording, 2-MPNQ (30 microM) applied intracellularly suppressed the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels but did not modify single channel conductance. Menadione (30 microM) had no effect on the channel activity, whereas 1,4-naphthoquinone (30 microM) suppressed it by about 26%. Both 2-MPNQ and thimerosal suppressed the dithiothreitol-stimulated channel activity. 2-MPNQ also blocked voltage-dependent K+ currents, but it produced a slight reduction of L-type Ca2+ inward current. However, unlike E-4031, 2-MPNQ (30 microM) did not suppress inwardly rectifying K+ current present in GH3 cells. Under the current clamp configuration, the presence of 2-MPNQ (30 microM) depolarized the cells, and increased the frequency and duration of spontaneous action potentials. The 2-MPNQ-mediated inhibition of K+ currents would affect hormone secretion and cell excitability. The blockade of these ionic channels by 2-MPNQ may partly explain its inhibitory effect on the proliferation of GH3 cells.

Ca2+-activated K+ currents (I(K(Ca)) can contribute to action potential repolarization and after-hyperpolarization in GH3 cells. In this study, we examined how the activation of I(K(Ca) at the cellular level could be functionally coupled to Ca2+ influx through L-type Ca2+ channels. A 30-msec Ca2+ influx step to 0 mV was found to exhibit substantial contribution of Ca2+ influx through the activation of I(Ca,L) to the activation of I(K(Ca)). A bell-shaped relationship between the conditioning potentials and the integrated I(K(Ca)) was observed, suggesting that the magnitude of integrated I(Ca,L) correlates well with that of integrated I(K(Ca)) in the same cell. A linear relationship of integrated I(Ca,L) and integrated I(K(Ca)) was found with a coupling ratio of 69+/-7. The value of the coupling ratio was unaffected by the presence of Bay K 8644 or nimodipine, although these compounds could effectively affect the amplitudes of both I(K(Ca)) and I(Ca,L). However, tetrandrine could decrease the coupling ratio. Paxilline or intracellular Ca2+ buffer with EGTA decreased the coupling ratio, while apamin had no effect on it. Interestingly, phorbol 12-myristate 13-acetate also reduced the coupling ratio significantly, whereas thapsigargin increased this value. Thus, the present study indicates that the activation of I(K(Ca)) during brief Ca2+ influx, which is inhibited by paxilline, is coupled to Ca2+ influx primarily through the L-type channels. The selective modulation of I(K(Ca)) by second messengers or Ca2+ release from internal stores may affect the coupling efficiency and hence cellular excitability.

Calcium (Ca2+) influx into human polymorphonuclear cells (PMNs) in response to N-formyl-Met-Leu-Phe (fMLP) and platelet-activating factor (PAF) stimulation was studied. Whole blood was taken by venous puncture from healthy human volunteers. PMNs were isolated, diluted, and incubated with 2 microM fura-2 AM. The cytosolic free calcium concentration, [Ca2+]i, in human neutrophils was determined by microfluorometry. We found that the net area under the fMLP- or PAF-induced [Ca2+]i rise curve in Ca2+-free medium decreased to 75% or 30% of the area under the curve in Ca2+ medium. Treatment of PMNs with phorbol myristate acetate (PMA), a protein kinase C activator, completely abolished the intracellular Ca2+ level stimulated by PAF, but not the intracellular Ca2+ level stimulated by fMLP. Treatment of PMNs with PAF did not abolish the intracellular Ca2+ level elevation stimulated by fMLP. In addition, treatment of PMNs with fMLP did not abolish intracellular Ca2+ level elevation stimulated by PAF. Loperamide, a positive modulator for store-operated calcium (SOC) channels, elicited an increase in intracellular calcium after the activation of SOC channels stimulated by fMLP or PAF. After the addition of guanosine 3',5'-cyclic monophosphate, N2,2'-O-Dibutyryl-, sodium salt (db-cGMP), the initial increase of PAF- or fMLP-induced PMNs intracellular Ca2+ fluorescences was well preserved, but the slope and the peak height of fluorescence curves declined compared with the curves without db-cGMP. In conclusion, we found that PAF and fMLP regulate the Ca2+ influx of PMNs in different ways. Most of the PAF-induced [Ca2+]i rise resulted from Ca2+ influx, and most of the fMLP-induced [Ca2+]i elevation resulted from intracellular stores release. The initial mobilization of intracellular Ca2+ stores in PAF-stimulated signals is mediated by protein kinase C (PKC) phosphorylation, but not in fMLP-stimulated route. SOC channels are present and important in the fMLP- or PAF-induced PMNs Ca2+ influx. There was no apparent cross-regulation between PAF- and fMLP-stimulated intracellular Ca2+ influx.

The ionic mechanism of clotrimazole, an imidazole antimycotic P-450 inhibitor, was examined in rat anterior pituitary GH3 cells. In perforated-patch whole-cell recording experiments, clotrimazole reversibly caused an inhibition of the Ca2+-activated K+ current in a dose-dependent manner. The IC50 value of the clotrimazole-induced inhibition of I(K(Ca)) was 3 microM. In the outside-out configuration of single channel recording, application of clotrimazole (10 microM) into the bath medium did not change the single channel conductance of large conductance Ca2+-activated K+(BK(Ca)) channels, but it suppressed the channel activity significantly. The change in the kinetic behavior of BK(Ca) channels caused by clotrimazole in these cells is found to be due to a decrease in mean open time and an increase in mean closed time. Other structurally distinct P-450 inhibitors (e.g. ketoconazole or econazole) also effectively suppressed the amplitude of I(K(Ca)). Clotrimazole (10 microM) blocked both the inactivating and non-inactivating components of the voltage-dependent K+ outward current (I(K(V))), but it produced a slight reduction of L-type Ca2+ inward current (I(Ca,L)) without altering the current-voltage relationship of I(Ca,L). Clotrimazole (10 microM) also increased the firing rate of action potentials. These results provide direct evidence that clotrimazole is capable of suppressing the activity of BK(Ca) channel in GH3 cells. Because of the non-selective inhibitory effect of clotrimazole on I(K(Ca)) and I(K(V)), this inhibition is mainly, if not entirely, due to a direct channel blockade. Thus, the present study implies that the blockade of these ionic channels by clotrimazole would affect hormonal secretion and neuronal excitability.

Primary angioplasty for acute myocardial infarction is frequently performed. Not uncommonly, more than one occluded artery may be present. Usually only one is an acute event, the others being chronic occlusions. We encountered a patient who presented with two simultaneous occlusions; both were successfully recanalized. We discuss some observations that assisted us in devising our treatment strategy.

Interest in Mannich bases of 8-hydroxyquinoline stems from reports of their high potency against human cancer cells. In the search for potential anticancer drug candidates, Mannich bases of 8-hydroxyquinoline (7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline, 7-piperidinomethyl-8-hydroxyquinoline and 7-diethylaminomethyl-8-hydroxyquinoline) were synthesised by reaction with various secondary amines and formaldehyde. They were prepared as hydrochlorides. The cytotoxic activity of 7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline and 7-diethylaminomethyl-8-hydroxyquinoline compounds in the National Cancer Institute in-vitro cancer cell line panel was determined. It was found that they exhibited substantial cytotoxic activity against leukaemia. The log concentration of 7-pyrrolidinomethyl-8-hydroxyquinoline, 7-morpholinomethyl-8-hydroxyquinoline and 7-diethylaminomethyl-8-hydroxyquinoline that inhibited 50% of 60 cell lines' growth were -4.81 M, -5.09 M and -5.35 M, respectively. Compound 7-pyrrolidinomethyl-8-hydroxyquinoline was selected for further in-vivo testing. The electrophysiological effect of 7-pyrrolidinomethyl-8-hydroxyquinoline also was tested in human myeloma cells (RPMI 8226). The outward current was voltage dependent, activating at -40 mV and believed to be the voltage-activated K+ current I(K(V)). 7-Pyrrolidinomethyl-8-hydroxyquinoline (1-30 microM) caused the inhibition of I(K(V)) in a concentration-dependent manner. The IC50 value of 7-pyrrolidinomethyl-8-hydroxyquinoline-induced inhibition of I(K(V)) is 23 microM. The GI50 value of 7-pyrrolidinomethyl-8-hydroxyquinoline-induced inhibition of cell growth is 14 microM. The results suggest that at least part of the cytotoxicity effect of 7-pyrrolidinomethyl-8-hydroxyquinoline on myeloma cells could be related to blockade of voltage-activated K+ channels.

We have investigated the inhibitory effect of 2-hydroxymethyl-1-naphthol diacetate (TAC) on the respiratory burst of rat neutrophils and the underlying mechanism of action was also assessed in this study. TAC caused concentration-related inhibition of the formylmethionyl-leucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2*-) generation (IC50 10.2+/-2.3 and 14.1+/-2.4 microM, respectively) and O2 consumption (IC50 9.6+/-2.9 and 13.3+/-2.7 microM, respectively) of neutrophils. TAC did not scavenge the generated O2*- during dihydroxyfumaric acid autoxidation. TAC inhibited both the transient elevation of [Ca2+]i in the presence or absence of [Ca2+]o (IC50 75.9+/-8.9 and 84.7+/-7.9 microM, respectively) and the generation of inositol trisphosphate (IP3) (IC50 72.0+/-9.7 microM) in response to fMLP. Cytosolic phospholipase C (PLC) activity was also reduced by TAC at a same range of concentrations. The PMA-induced PKC-beta associated to membrane was attenuated by TAC (about 80% inhibition at 30 microM). Upon exposure to fMLP, the cellular cyclic AMP level was decreased in neutrophils pretreated with TAC. TAC attenuated fMLP-induced phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 (IC50 17.4+/-1.7 microM), but not p38. The cellular formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) induced by fMLP was inhibited by TAC in a concentration-dependent manner (IC50 25.4+/-2.4 and 25.9+/-1.4 microM, respectively). TAC had no effect on the O2*- generation of PMA-stimulated and arachidonic acid (AA)-stimulated NADPH oxidase preparations. However, TAC caused concentration-related decrease of the membrane associated p47phoX in PMA-stimulated neutrophils (about 80% inhibition at 30 microM). We conclude that inhibition by TAC of the neutrophil respiratory burst is probably attributable to the blockade of the p42/44 MAPK and phospholipase D (PLD) pathways, the membrane translocation of PKC, and to the failure in assembly of a functional NADPH oxidase complex. Blockade of the PLC pathway by TAC probably plays a minor role.

1-Pyrrolidinylmethyl-2-naphthol hydrochloride (TPY-beta) has been reported to have hypotensive and bradycardiac effects in anesthetized rats. Whether administration of atropine or bilateral vagotomy affects mean arterial pressure or heart rate was examined. The percentage difference in hypotensive and bradycardiac effect of TPY-beta (0.5 mg/kg) was 63 +/- 5% and 68 +/- 9%, respectively, in unpretreated rats compared to control levels. Atropine pretreatment (0.1 mg/kg, i.v.) significantly reduced the depressant effect of TPY-beta, although heart rate and mean arterial pressure remained 21 +/- 3% and 31 +/- 4%, respectively, as compared to control levels. Vagotomy decreased heart rate and mean arterial pressure response but moderate bradycardiac (13 +/- 2%) and hypotensive (10 +/- 3%) effects still remained as compared to control levels. Unilateral microinjection of 1, 3.3 and 10 nM TPY-beta into the nucleus tractus solitarri elicited a dose-dependent depressor (-10 +/- 2; -20 +/- 3; -25 +/- 3 mmHg) and bradycardiac activities (-20 +/- 4; -26 +/- 5; -55 +/- 10 beats/min). TPY-beta also relaxed the isolated rat aortic rings preconstracted with high extracellular K+ (80 mM) and Ca2+ (1.9 mM). The above findings suggest that the suppressive effects of TPY-beta may involve activation of vagus nerve and a direct inhibition of Ca2+ channel. In addition, TPY-beta inhibited the aggregation of washed rabbit platelets (aggregated by arachidonic acid and collagen) and adhesiveness on fibrinogen-coated surface. The results suggest that TPY-beta possesses antihypertensive and antiplatelet activity.

As widely assumed, platelets and coagulation system heavily influence the pathogenesis and progression of cardiovascular diseases. Some 1,4-naphthoquinone derivatives, such as vitamin K3, have been reported to increase the synthesis of coagulation proteins. In this study, we examine how 2-p-mercaptophenyl -1,4-naphthoquinone (NTP), a newly synthesized 1,4-naphthoquinone derivative, affects the platelet function in humans. A tapered parallel plate chamber which provided a range of shear stress covering the entire physiological range in human circulation is used to assess platelet adhesiveness on fibrinogen coated-surface. In addition, platelet aggregation and thromboxane B2 (TXB2) production by inducers are evaluated by the turbidimetric method and enzyme immunoassay kit, respectively. Moreover, platelets [Ca2+]i are measured using a dual-wavelength fluorescence spectrophotometer. Analysis results indicate that 1) NTP decreases the percentages of attached platelets at the locations in various shear stresses and the levels of platelet adhesiveness, denoted as the slope; 2) NTP can inhibit the platelet aggregation by ADP (2 microM) and collagen (25 microg/ml), and the IC50 are: 0.32 and 26.83 microg/ml, respectively; and 3) NTP markedly inhibits TXB2 formation and platelet [Ca2+]i elevation caused by ADP and collagen. Therefore, we conclude that NTP may inhibit platelet adhesiveness on fibrinogen coated-surface, aggregability, [Ca2+]i, and thromboxane production, and that it may be used as an antiplatelet agent.

7-Morpholinomethyl-8-hydroxyquinoline (MO-8HQ), which like 8-hydroxyquinoline (8HQ) readily forms a chelate, was synthesized and found to possess cytotoxicity and antimicrobial activity. Both 8HQ and MO-8HQ were cytotoxic to human carcinoma cell lines at micromolar concentrations. MO-8HQ also inhibited DNA synthesis of tumor cells at micromolar concentrations, suggesting that MO-8HQ might chelate metals necessary for the enzymatic catalysis of DNA biosynthesis. MO-8HQ was more active against gram positive bacteria than gram negative bacteria and its potency correlated with iron chelation. An "unsaturated" chelate with a MO-8HQ to Fe ratio of 2:1 exhibited greater antibacterial activity than MO-8HQ alone. Among the organisms tested, Micrococcus flavus was most susceptible with a MIC of 3.9 microg/ml. MO-8HQ also exhibited anti-fungal activity at 7-15 microg/ml. MO-8HQ:Fe chelate markedly increased the susceptibility of Escherichia coli to deoxycholate. Addition of Ca2+ or Mg2+ reversed the sensitivity of bacteria to deoxycholate as well as to rifampicin. It is suggested that MO-8HQ exerts its biological activity as a membrane-active agent through metal ion chelation.

Two different types of nonselective cation currents in monocytic U937 cells were characterized with the aid of patch-clamp technique. When the cells were exposed to oxidative stress with 10 mM H2O2, a nonselective cation current (INS) can be elicited. This current was still observed when extracellular cations are Ca2+. The change in intracellular Cl- concentrations did not shift the reversal potential of this current. This current showed no any rectification, and was time- and voltage-independent at any potentials. The further addition of LaCl3 (100 microM) or dithiothreitol (10 microM) effectively suppressed this current. However, SK & F 96365 (100 microM) or nifedipine (10 microM) did not produce any effect on it significantly. On the other hand, depletion of Ca2+ stores by different maneuvers, such as the application of ATP, thapsigargin or A23187, or dialysis of the cells with inositol-1,4,5-trisphosphate activated another type of nonselective current which was identified as store-operated Ca(2+)-permeable current (ISOC). Unlike H2O2-induced INS, this current was observed to slowly inactivate when the voltage steps were hyperpolarized. Current-voltage relation of this current showed inward rectification. When the cell was challenged with both store depletion and H2O2, INS on the top of ISOC can be activated. These results suggest that different types of nonselective cation channels can be co-expressed in the same cell. Therefore, in U937 cells nonselective cation currents can be activated after the stimulation with oxidative stress, store depletion or both. The activation of these nonselective cation channels may affect intracellular Ca2+ homeostasis.

Twenty-three patients with angiographically documented total occlusion of the left main coronary artery were retrospectively identified. Statistical analysis suggests that poor right-to-left collaterals and the presence of concurrent significant right coronary artery disease were weakly associated with decreased survival after bypass surgery.

The cardiovascular activity of TPI in lowering the blood pressure and heart rate in anesthetized rats was studied using pharmacological and physiological techniques. The hypotensive and bradycardiac actions induced by a bolus intravenous injection were significantly inhibited by pretreatment with atropine (0.1 mg/kg; i.v.). Vagotomy almost abolished the hypotensive response but moderate bradycardia still remained. Microinjection of TPI (1-10 nmol) into the nucleus tractus solitarii of brain stem produced a prominent dose related hypotensive and bradycardic effects. TPI also produced a decrease in the force of contraction of the isolated right atrium of guinea pig. These results suggest that the effects of TPI may involve an activation of the vagus nerve and suppressive action on myocardial tissue.

Mechanical restitution and post-rest potentiation in isolated rat atria were studied in order to understand the intracellular Ca2+ handling during stimulation and interbeat interval. Various agents known to affect transmembrane Ca2+ inward current or Ca2+ accumulation of the sarcoplasmic reticulum were examined. The tissues were stimulated at 1 Hz and ectopic stimuli of different preceding intervals were driven by a programmable stimulator. The relationship between the force produced by the ectopic contraction and the duration of the preceding interval was plotted to construct mechanical restitution curves. Mechanical restitution curve was well fitted to two exponential processes, i.e., an early rapid phase followed by a slowly rising phase. It is suggested that the time constant in early phase (tau 1) of mechanical restitution curve is dependent on the reactivation of transmembrane Ca2+ inward currents as well as the translocation of Ca2+ within the sarcoplasmic reticulum. However, the time constant in late phase (tau 2) involves the rate of Ca2+ influx or efflux possibly via the Na+/Ca2+ exchange mechanism. The present studies suggest that in rat myocardium, verapamil enhances the buffering capacity of the sarcoplasmic reticulum inside the cell, while isoproterenol appears to short circuit the buffering barrier of the sarcoplasmic reticulum and enhance the flow of Ca2+ into the cytosol. Ryanodine, which accelerates the Ca2+ release from the sarcoplasmic reticulum, is believed to attenuate its buffering capacity. The present analytical methods to which the mechanical restitution and the post-rest potentiation are combined would represent a good model for the study of beat-to-beat intracellular Ca2+ handling in cardiac muscle.

2-Hydroxymethyl-1-naphthol diacetate (TAC) and sixteen Mannich base derivatives of naphthol were prepared and examined for cytotoxicity and antimicrobial activity. Cytotoxicity was examined against four human carcinoma cell lines. Several derivatives were effective at concentrations < 4 micrograms/ml. TAC showed the highest cytotoxicity. Inhibition of DNA-, RNA-, and protein synthesis by TAC was also studied and discussed. TAC also exhibits potent antimicrobial activity against Enterobacter clocae 23355, Klebsiella pneumonia 13883, Proteus vulgaris 13315, Pseudomonas aeruginosa 27853, Candida parapsilosis, Candida tropicalis, Trichosposon beigelli, and Rhodotorul spp. with minimum inhibitory concentrations of 0.1-0.4 microM. These results indicate that esterification by Bruson reaction of 1-naphthol Mannich base to TAC enhances the cytotoxicity and antimicrobial activity.

Neural connections from the hippocampus and nucleus accumbens to the subpallidal area have been implicated by behavioral observation. The locomotor activity recorded in an automated activity cage increased substantially after the bilateral injection of carbachol, a cholinergic agonist, into the dentate gyrus of the hippocampus, and this increase of activity was reduced significantly after the injection of glutamate antagonist into the nucleus accumbens. On the other hand, this hyperactivity elicited by the injection of carbachol was also reduced by the injection of GABA into the subpallidal area. In another observation, increased locomotor activity was recorded following the injection of dopamine into the nucleus accumbens. However, the increase of locomotor activity induced by dopamine was attenuated by the injection of GABA into the subpallidal area. These observations suggest that neural connections from hippocampus and nucleus accumbens to the subpallidal region may contribute to locomotor activity.

Malaria chemotherapy has been well reviewed. Malarial parasites gaining resistance is the major problem in the treatment of the disease. Some strains are resistant not only to chloroquine but also to amodiaquine. Few new drugs are available or foreseen for the near future. The principal metabolite of cinchona alkaloids appears to be oxidized at C-2. This may result in a loss of activity. Pinder and Burger suggested that a trifluoromethyl group will prevent this oxidation. So 2-tribromomethyl-6-methoxy-4-(4-hydroxy-3-pyrrolidinomethylanil ino)quinoline (1) was synthesized as a potential biocide (Scheme 1).

A series of guaiacoxypropanolamine derivatives of capsaicin was synthesized by replacing the phenolic OH of N-nonanoylvanillamide with epichlorohydrin, followed by cleavaging the obtained epoxide compound with alkylamines. Intravenous injection of these propanolamine derivatives (1 mg/kg) in normotensive Wistar rats induced a transient fall in blood pressure but significantly reduced the heart rate for more than 30 min. These derivatives (10(-8)-10(-6) M) inhibited isoproterenol (10(-10)-10(-5) M)-induced positive chronotropic and inotropic effects in isolated guinea pig atrium. On the other hand, these derivatives (10(-5)-10(-4) M) exhibited a positive cardiotonic effect that is independent of intrinsic sympathomimetic effects. Investigation of the structure-activity relationship of these derivatives revealed that the position of the oxypropanolamine side chain and substituents of the 4-OH position play significant roles in imparting their pharmacological effects. Of the derivatives tested, the most effective one was compound 9. In conclusion, the results obtained from in vitro and in vivo studies suggested that these derivatives and compound 9 may be expected to be beta-adreneoceptor blocking agents with nonadrenergic positive chronotropic and inotropic properties.

In anesthetized rats, intravenous injection of 1-(1-pyrrolidinylmethyl)-2-naphthol (TPY-beta, 0.1-1 mg/kg) induced a transient (less than 1 min) decrease in arterial blood pressure and heart rate (acute responses) followed by a delayed and sustained (greater than 10 min) bradycardic response. The electrophysiological mechanisms responsible for the bradycardic effect of TPY-beta were studied in sinoatrial tissues isolated from guinea-pig hearts. Transmembrane action potential (AP) and twitch force of atrial tissues were recorded with the conventional microelectrode techniques. In sinoatrial pacemakers active spontaneously in 4 mM [K]o Tyrode solution, TPY-beta (3-100 microM) depressed the diastolic slope and the rate of spontaneous discharges. When the non-automatic atrial tissues were driven at a fixed rate, TPY-beta (10-100 microM) inhibited the upstroke velocity of phase-0 depolarization and prolonged AP duration. In atrial fibers depolarized in high [K]o (24 mM), TPY-beta depressed the phase-0 upstroke of slow response AP and the twitch force in a concentration-dependent manner. The present results indicate that TPY-beta induced direct negative chronotropic and inotropic effects on guinea-pig atrial pacemakers and myocardial fibers. The underlying mechanisms involve a general inhibition of transmembrane of Ca, K and Na ion fluxes.