It was attempted to clarify the participation of K+ channels in the post-receptor mechanisms of the muscarinic and A1-adenosine receptor-mediated control of acetylcholine (ACh) release in the present study. Slices from the rat hippocampus were equilibrated with (3H)choline and the release of the labelled products was evoked by electrical stimulation (3 Hz, 5 V/cm, 2 ms, rectangular pulses), and the influence of various agents on the evoked tritium-outflow was investigated. Oxotremorine (Oxo, 0.1~10 micrometer), a muscarinic agonist, and N6-cyclopentyladenosine (CPA, 1~30 micrometer), a specific A1-adenosine agonist, decreased the ACh release in a dose-dependent manner, without affecting the basal rate of release. 4-aminopyridine (4AP), a specific A-type K+-channel blocker (1~100 micrometer), increased the evoked ACh release in a dose-related fashion, and the basal rate of release is increased by 3 and 100 micrometer. Tetraethylammonium (TEA), a non-specific K+-channel blocker (0.1~10 mM), increased the evoked ACh release in a dose-dependent manner without affecting the basal release. The effects of Oxo and CPA were not affected by 3 micrometer 4AP co-treatment, but 10 mM TEA significantly inhibited the effects of Oxo and CPA. 4AP (10 micrometer- and TEA (10 mM)-induced increments of evoked ACh release were completely abolished in Ca2+-free medium, but these were recovered in low Ca2+ medium. And the effects of K+-channel blockers in low Ca2+ medium were inhibited by Mg2+ (4 mM) and abolished by 0.3 micrometer tetrodotoxin (TTX). These results suggest that the changes in TEA-sensitive potassium channel permeability and the consequent limitation of Ca2+ influx are partly involved in the presynaptic modulation of the evoked ACh-release by muscarinic and A1-adenosine receptors of the rat hippocampus.
4-Aminopyridine ; Acetylcholine* ; Animals ; Electric Stimulation ; Hippocampus* ; Muscarinic Agonists ; Oxotremorine ; Permeability ; Potassium Channels ; Rats* ; Receptors, Muscarinic ; Tea ; Tetraethylammonium ; Tetrodotoxin

There are some evidences that K+ efflux evoked by muscarinic stimulation is not mainly mediated by large conductance K+ (BK) channels in salivary gland. In this experiment, we therefore characterised non BK channels in rat submandibular gland acinar cells and examined the possibility of agonist effect on this channel using a patch clamp technique. Two types of K+ channels were observed in these cells. BK channels were observed in 3 cells from total 6 cells and its average conductance was 152+/- 7 pS (n=3). The conductance of the another types of K+ channel was estimated as 71+/-7 pS (n=6). On the basis of the conductance of this channel, we defined this channel as intermediate conductance K+ (IK) channels, which were observed from all 6 cells we studied. When we increased Ca2+ concentration of the bath solution in inside-out mode, the IK channel activity was greatly increased, suggesting this channel is Ca2+ sensitive. We next examined the effect of carbachol (CCh) and isoproterenol on the activity of the IK channels. 10(-5) M isoproterenol significantly increased the open probability (Po) from 0.08+/-0.02 to 0.21+/-0.03 (n=4, P<0.05). Application of 10(-5) M CCh also increased Po from 0.048+/-0.03 to 0.55+/-0.33 (n=5, P<0.05) at the maximum channel activity. The degree of BK channel activation induced by the same concentration of CCh was lower than that of IK channels; Po value was 0.011+/-0.003 and 0.027+/-0.005 in control and during CCh stimulation (n=3), respectively. The result suggests that IK channels exist in salivary acinar cells and its channel activity is regulated by muscaricinic and beta- adrenergic agonist. We conclude that IK channels also play a putative role in secretion as well as the BK channels in rat submandibular gland acinar cells.
Acinar Cells* ; Adrenergic Agonists ; Animals ; Baths ; Carbachol ; Isoproterenol ; Large-Conductance Calcium-Activated Potassium Channels ; Rats ; Salivary Glands ; Submandibular Gland*

BACKGROUND AND OBJECTIVES: This study was aimed to explore the effects of the 5-hydroxytryptamine (5-HT) on potassium currents in rat vestibular nuclear neurons. MATERIALS AND METHOD: Sprague-Dawley rats aged 14 to 16 days were anesthetized with ether and decapitated. After enzymatic digestion, the portion of medial vestibular nucleus neuron was removed by micropunching and gently agitated. The dissociated neurons were transferred into a recording chamber mounted on an inverted microscope and whole-cell membrane currents were recorded at room temperature by using standard patch-clamp techniques. RESULTS: When cells were held at -70 mV and depolarized from -60 mV to +40 mV in 10 mV increments, sustained outward potassium currents were evoked. The response of medial vestibular nuclear neurons to 5-HT was not uniform. The outward potassium currents were increased in 17 of 40 cells and decreased in 23 of 40 cells. 5-carboxamidotryptamine, 5-HT1 agonist increased the outward potassium currents of the medial vestibular nuclear cell. alpha-methyl-5-hydroxytryptamine, 5-HT2 agonist decreased the outward potassium currents of the medial vestibular nuclear cell. CONCLUSION: These results suggest that 5-HT affects the potassium currents of the cell with different effects according to the receptor subtype on which it acts.
Animals ; Digestion ; Dihydroergotamine ; Ether ; Membranes ; Neurons* ; Patch-Clamp Techniques ; Potassium Channels ; Potassium* ; Rats* ; Rats, Sprague-Dawley ; Serotonin 5-HT1 Receptor Agonists ; Serotonin 5-HT2 Receptor Agonists ; Serotonin* ; Vestibular Nuclei

This study was designed to characterize ureteral smooth muscle motility and also to study the effect of forskolin (FSK) and isoproterenol (ISO) on smooth muscle contractility in murine ureter. High K+ (50 mM) produced tonic contraction by 0.17+/-0.06 mN (n=19). Neuropeptide and neurotransmitters such as serotonin (5microM), histamine (20microM), and carbarchol (CCh, 10~50microM) did not produce significant contraction. However, CCh (50microM) produced slow phasic contraction in the presence of 25 mM K+. Cyclopiazonic acid (CPA, 10microM), SR Ca2+-ATPase blocker, produced tonic contraction (0.07 mN). Meanwhile, inhibition of mitochondria by protonophore carbnylcyanide m-chlorophenylhydrazone (CCCP) also produced weak tonic contraction (0.01 mN). The possible involvement of K+ channels was also pursued. Tetraethyl ammonium chloride (TEA, 10 mM), glibenclamide (10microM) and quinidine (20 microM) which are known to block Ca2+-activated K+ channels (KCa channel), ATP-sensitive K+ channels (KATP) and nonselective K+ channel, respectively, did not elicit any significant effect. However, Ba2+ (1~2 mM), blocker of inward rectifier K+ channels (KIR channel), produced phasic contraction in a reversible manner, which was blocked by 1microM nicardipine, a blocker of dehydropyridine-sensitive voltage-dependent L-type Ca2+ channels (VDCCL) in smooth muscle membrane. This Ba2+-induced phasic contraction was significantly enhanced by 10microM cyclopiazonic acid (CPA) in the frequency and amplitude. Finally, regulation of Ba2+-induced contraction was studied by FSK and ISO which are known as adenylyl cyclase activator and beta-adrenergic receptor agonist, respectively. These drugs significantly suppressed the frequency and amplitude of Ba2+-induced contraction (p<0.05). These results suggest that Ba2+ produces phasic contraction in murine ureteral smooth muscle which can be regulated by FSK and beta-adrenergic stimulation.
Adenylyl Cyclases ; Adrenergic beta-Agonists ; Ammonium Chloride ; Colforsin ; Glyburide ; Histamine ; Isoproterenol ; Membranes ; Mitochondria ; Muscle, Smooth* ; Neuropeptides ; Neurotransmitter Agents ; Nicardipine ; Potassium Channels, Calcium-Activated ; Potassium Channels, Inwardly Rectifying ; Quinidine ; Serotonin ; Ureter*

OBJECTIVETo investigate the mechanism of ATP-sensitive potassium channel (K(ATP)) activator cromakalim (CRK) on action potentials and transient inward current (I(ti)) in isolated guinea pig papillary and ventricular myocytes and to explore the mechanisms of effects of I(ti) and K(ATP) treatment in idiopathic ventricular tachycardia.

METHODSThe whole-cell patch clamp recording technique was used to detect the action potentials and I(ti) and K(ATP) current alterations during the stimulated and triggered activity. Myocytes were isolated from guinea pig ventricle by enzyme digestion. The experiment was divided into four groups: (1) Control; (2) Control + Ouabain; (3) Control + CRK; (4) Control + Ouabain + CRK. (5) Control + Ouabain + CRK + glibenclamide (GLB). The action potential of guinea pig papillary muscles was measured by using standard microelectrode. The parameters in the experiment included the amplitude (APA), resting potentials (RP), action potentials duration (APD), as well as maximum rise of the action potential (Vmax).

RESULTS(1) When the guinea pig ventricular papillary myocytes were pretreated with Ouabain 0.5 micromol/L, APD prolonged significantly, especially APD(20), APD(50), APD(90). Delayed after depolorazion (DAD) and triggered activity were elicited. I(ti) currents and DAD as well as triggered activity increased. I(ti) current was (126.9 +/- 10.8) pA, lagT (1173.0 +/- 70.9) ms (n = 10, P < 0.01). (2) When guinea pig ventricular myocytes were pretreated with CRK (10 micromol/L), APD was shortened and the amplitude of DAD was lowered. The coupling time in CRK group was significantly prolonged compared with Ouabain group (n = 10, P < 0.01). (3) CRK 50 micromol/L pretreatment of the ventricular myocytes led to an increase of K(ATP) up to (342 +/- 89) pA, which was statistically significant as compared with the control group (P < 0.01). ATP-sensitive potassium channel blocker glibenclamide (10 micromol/L) could antagonize the effects of CRK on APD and I(ti) currents.

CONCLUSIONCRK might reduce the toxic effect of Ouabain on cardiomyocytes, shorten APD, terminate DAD and trigger excitation, and have protective effect on cardiomyocytes. The effects of CRK, may be associated with the inhibiting I(ti) current and increasing K(ATP).

Action Potentials ; drug effects ; Animals ; Cromakalim ; pharmacology ; Guinea Pigs ; Heart Ventricles ; drug effects ; Myocytes, Cardiac ; drug effects ; physiology ; Patch-Clamp Techniques ; Potassium Channels, Inwardly Rectifying ; agonists

AIMIn search of more potent, less toxic and selective potassium channel openers.

METHODSAccording to the structure-activity relationships of benzopyran compounds and the features of structures of aprikalim, dofetilide and nifekalant, twenty benzopyran-4-one hydrazone derivatives have been designed and synthesized from 4-cyanophenos through acetylation, Fries rearrangment, cyclization, hydrazone, substitution reaction and so on. The compounds were tested for their vasorelaxant activity in low (30 mmol.L-1) and high (80 mmol.L-1) KCl-induced contraction of rat aorta to identify potential potassium channel openers in vitro.

RESULTSThree series of twenty benzopyran-4-one hydrazone derivatives, nominated N-aminoacetyl-(6-cyano-3,4-dihydrospiro [2H-1-benzopyran-2,1'-cyclohexane]-4)-one hydrazone (I), 2-(6-cyano-3, 4-dihydro-2H-1-benzopyran-4-ylene) hydrazinethiocarboxamide derivatives (II) and N-(2-arylethyl) aminoacetyl-(6-cyano-3,4-dihydro-2H-1-benzopyran)-4-one hydrazone (III), have been synthesized. They (I1-9, II1-4 and III1-7) are new compounds. Their chemical structures were determined by IR, 1HNMR, MS and elemental analysis. The vasorelaxant effects of those novel compounds indicated that some of the compounds have vasorelaxant activities at 1 x 10(-6) mol.L-1.

CONCLUSIONThe vasorelaxant activities of compounds I9, III2 and III5 in inhibiting low KCl-induced vasocontraction at 1 x 10(-6) mol.L-1 are less potent than the reference compound emakalim. However they are more potent than emakalim to inhibition high concentration KCl-induced vasocontraction at 1 x 10(-5) mol.L-1. It is worthy of further study.

Animals ; Aorta ; drug effects ; Benzopyrans ; chemical synthesis ; pharmacology ; Molecular Structure ; Potassium Channels ; agonists ; Rats ; Vasodilation ; drug effects ; Vasodilator Agents ; chemical synthesis ; pharmacology

In the present study, whole-cell patch-clamp technique was used to observe the effects of SNC162, a selective agonist of δ-opioid receptors, on L-type Ca(2+) current (I(Ca-L)) and transient outward K(+) current (I(to)) in rat ventricular myocytes. The results showed that SNC162 significantly inhibited I(Ca-L) and I(to) in rat ventricular myocytes. The maximal inhibition rate of I(Ca-L) and I(to) reached (46.13±4.12)% and (36.53±10.57)%, respectively. SNC162 at 1×10(-4) mol/L inhibited the current density of I(Ca-L) from (8.98±0.40) pA/pF to (4.84±0.44) pA/pF (P<0.01, n=5) and inhibited that of I(to) from (18.69±2.42) pA/pF to (11.73±1.67) pA/pF (P<0.01, n=5). Furthermore, the effects of naltrindole, a highly selective antagonist of δ-opioid receptors, on I(Ca-L) and I(to) were also observed. The results showed that naltrindole alone had no effects on I(Ca-L) and I(to), while it abolished the inhibitory effects of SNC162 on I(Ca-L) and I(to). In conclusion, SNC162 concentration-dependently inhibited I(Ca-L) and I(to) in rat ventricular myocytes via activation of the δ-opioid receptors, which may be a fundamental mechanism underlying the antiarrhythmic effect of activating δ-opioid receptors.
Animals ; Anti-Arrhythmia Agents ; Benzamides ; pharmacology ; Calcium Channels, L-Type ; metabolism ; Cells, Cultured ; Heart Ventricles ; cytology ; Myocytes, Cardiac ; drug effects ; metabolism ; Naltrexone ; analogs & derivatives ; pharmacology ; Patch-Clamp Techniques ; Piperazines ; pharmacology ; Potassium Channels ; metabolism ; Rats ; Receptors, Opioid, delta ; agonists

The aim of the present study was to study the effect of β-estradiol (β-E(2)) on the large-conductance Ca(2+)-activated potassium (BK(Ca)) channel in mesenteric artery smooth muscle cells (SMCs). The mesenteric arteries were obtained from post-menopause female patients with abdominal surgery, and the SMCs were isolated from the arteries using an enzymatic disassociation. According to the sources, the SMCs were divided into non-hypertension (NH) and essential hypertension (EH) groups. Single channel patch clamp technique was used to investigate the effect of β-E(2) and ICI 182780 (a specific blocker of estrogen receptor) on BK(Ca) in the SMCs. The results showed the opening of BK(Ca) in the SMCs was voltage and calcium dependent, and could be blocked by IbTX. β-E(2) (100 μmol/L) significantly increased open probability (Po) of BK(Ca) in both NH and EH groups. After β-E(2) treatment, NH group showed higher Po of BK(Ca) compared with EH group. ICI 182780 could inhibit the activating effect of β-E(2) on BK(Ca) in no matter NH or EH groups. These results suggest β-E(2) activates BK(Ca) in mesenteric artery SMCs from post-menopause women via estrogen receptor, but hypertension may decline the activating effect of β-E(2) on BK(Ca).
Aged ; Estradiol ; analogs & derivatives ; pharmacology ; Female ; Humans ; Hypertension ; physiopathology ; Large-Conductance Calcium-Activated Potassium Channels ; agonists ; metabolism ; physiology ; Mesenteric Arteries ; metabolism ; physiology ; Middle Aged ; Muscle, Smooth, Vascular ; cytology ; metabolism ; physiology ; Patch-Clamp Techniques ; Postmenopause ; physiology ; Receptors, Estrogen ; antagonists & inhibitors

Animals ; Delayed Rectifier Potassium Channels ; physiology ; Humans ; Membrane Potentials ; drug effects ; Myocardial Ischemia ; pathology ; physiopathology ; Pilocarpine ; pharmacology ; Piperidines ; pharmacology ; Receptor, Muscarinic M3 ; agonists ; antagonists & inhibitors ; physiology ; Signal Transduction ; drug effects

OBJECTIVETo explore the effects of iptkalim on myocardial enzymes and free radicals metabolism with hypoxic pulmonary hypertension (HPH), in order to provide evidence for the mechanism of iptkalim on clinical treat.

METHODS110 young men stayed at high altitude above 5 000 m were divided into iptkalim group (n = 74) and placebo group (n = 36), aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyltransferase (gamma-GT), creatine kinase (CK), lactate dehydrogenase (LDH), superoxide dismutase (SOD), malonaldehyde (MDA), nitric oxide(NO) and nitric oxide synthase(NOS) were detected before and after took medicines for 6 mouths.

RESULTSAfter took medication for 6 mouths, ALT, AST, gamma-GT, CK and LDH were reduced, SOD, NO, and NOS were increased, MDA were reduced, there were very significant difference (P < 0.05).

CONCLUSIONOxygen free radicals have taken part in the process of HPH, iptkalim have the effect of anti-peroxidation of lipid and protect myocardial cells stress injured by hypoxia which related with mitochondrial membrane and cell membrane's K(ATP) channel activation.

Adolescent ; Adult ; Altitude ; Creatine Kinase ; blood ; Free Radicals ; metabolism ; Humans ; Hypertension, Pulmonary ; blood ; etiology ; metabolism ; Hypoxia ; complications ; L-Lactate Dehydrogenase ; blood ; Male ; Myocardium ; enzymology ; Potassium Channels ; agonists ; Propylamines ; pharmacology ; Young Adult