AIMTo investigate the effect of benzyltetrahydropalmatine (BTHP) on the rapidly activating component of delayed rectifier K+ current (Ikr) in single guinea pig ventricular myocytes.

METHODSWhole-cell patch clamp technique was used to record Ikr.

RESULTSIkr was blocked by 1-100 mumol.L-1 BTHP in concentration-, voltage-, and specifically frequency-dependent fashion, with IC50 of 13.5 mumol.L-1 (95% confidence range: 11.2-15.8 mumol.L-1). 30 mumol.L-1 BTHP reduced Ikr and Ikr.tail by (31 +/- 4)% and (36 +/- 5)% (n = 6, P < 0.01), respectively. The time constant for deactivation (tau') of the tail current was decreased by 30 mumol.L-1 BTHP from (238 +/- 16) ms to (196 +/- 14) ms, while drug had no any effect on the time constant for activation (tau) of Ikr,tail.

CONCLUSIONBTHP inhibited Ikr in a frequency-dependent fashion.

Animals ; Anti-Arrhythmia Agents ; pharmacology ; Berberine Alkaloids ; pharmacology ; Cell Separation ; Delayed Rectifier Potassium Channels ; Female ; Guinea Pigs ; Heart Ventricles ; cytology ; metabolism ; Male ; Myocytes, Cardiac ; drug effects ; metabolism ; Patch-Clamp Techniques ; Potassium Channels ; drug effects ; metabolism ; Potassium Channels, Voltage-Gated

AIMTo study the effect of magnesium sulfate on transient outward K+ current (IA) and delayed rectifier K+ current (IK) in freshly dissociated hippocampal neurons of rats.

METHODSThe whole-cell patch clamp techniques were used.

RESULTSMagnesium sulfate reversibly reduced the amplitudes of IA and IK in a concentration-dependent and voltage-dependent, but not frequency-dependent manner. Half-blocking concentration (IC50) on IA and IK were 6.30 mmol.L-1 and 7.60 mmol.L-1, respectively. Magnesium sulfate (6 mmol.L-1) affected the activation process of IA and IK. Before and after application of the drug, the half-activation voltages of IA were (7 +/- 6) mV and (-7 +/- 11) mV (n = 10, P < 0.01), and the half-activation voltages of IK were (20 +/- 6) mV and (28 +/- 4) mV (n = 10, P < 0.01), but the slope factors were not changed. In addition, magnesium sulfate (6 mmol.L-1) also affected the inactivation process of IA. Before and after application of the drug, the half-inactivation voltages of IA were (-65 +/- 5) mV and (-89 +/- 6) mV (n = 10, P < 0.01).

CONCLUSIONMagnesium sulfate inhibited IA and IK in freshly dissociated hippocampal neurons of rats, which might contribute to protect the central neuronal system (CNS) against damages induced by ischemia and oxygen deprivation.

Animals ; Cell Separation ; Delayed Rectifier Potassium Channels ; Female ; Hippocampus ; cytology ; Magnesium Sulfate ; pharmacology ; Male ; Neurons ; drug effects ; physiology ; Neuroprotective Agents ; pharmacology ; Patch-Clamp Techniques ; Potassium Channels ; drug effects ; metabolism ; Potassium Channels, Voltage-Gated ; Rats ; Rats, Wistar

This study was carried out in adult ferret cardiomyocytes to investigate the effects of the n-3 polyunsaturated fatty acids (PUFAs) on voltage-gated K(+) currents. We report that the two outward K(+) currents: the transient outward K(+) current (I(to)) and the delayed rectifier K(+) current (I(K)), are both inhibited by the n-3 PUFAs, while the inwardly rectifying K(+) current (I(K1)) is unaffected by the n-3 PUFAs. Docosahexaenoic acid (C22:6n-3, DHA) produced a concentration dependent suppression of I(to) and I(K) in adult ferret cardiomyocytes with an IC(50) of 7.5 and 20 micromol/L, respectively; but not I(K1). In addition, eicosapentaenoic acid (C20:5n-3, EPA) had the effects on the three K(+) channels similar to DHA. Arachidonic acid (C20:4n-6, AA) at 5 or 10 micromol/L, after an initial inhibitory effect on I(K), caused an activation of I(K),AA which was prevented by pretreatment with indomethacin, a cyclooxygenase inhibitor. Monounsaturated and saturated fatty acids, which are not antiarrhythmic, lack the effects on these K(+) currents. Our results demonstrate that the n-3 PUFAs inhibit cardiac I(to) and I(K) with much less potency compared to their effects on cardiac Na(+) and Ca(2+) currents as we reported previously. This inhibition of the cardiac ion currents by the n-3 PUFAs may contribute to their antiarrhythmic actions.
Animals ; Arachidonic Acid ; pharmacology ; Docosahexaenoic Acids ; pharmacology ; Dose-Response Relationship, Drug ; Eicosapentaenoic Acid ; pharmacology ; Ferrets ; Myocytes, Cardiac ; drug effects ; metabolism ; Potassium Channels, Voltage-Gated ; metabolism

AIMTo investigate mRNA expression changes of voltage-gated outward potassium channel subtypes in cultured rat hippocampal neurons after chronic exposure to beta-amyloid-petitde25-35 (beta-AP25-35).

METHODSmRNA expression was detected by RT-PCR, comparative expression levels were determined by imaging densitometer.

RESULTSDelayed rectifying (Kv2.1, Kv1.5), transient outward (Kv1.4, Kv4.2) and large conductance calcium-activated (rSlo) potassium channel mRNA were expressed in cultured rat hippocampal. In the presence of beta-AP25-35 3 mumol.L-1 for 24 h, the relative expression level of Kv2.1 was significantly increased (n = 3, P < 0.05); the other subtypes were not changed obviously (n = 3, P > 0.05). The increase of Kv2.1 mRNA mainly happened between 24 and 36 h after exposure to beta-AP25-35. After exposure to beta-AP25-35 for 60 h, Kv2.1 mRNA decreased significantly (n = 3, P < 0.01).

CONCLUSIONThe upregulation of Kv2.1 on transcription levels may be involved in the enhancement of delayed rectifying outward potassium (Ik) current induced by beta-AP25-35.

Amyloid beta-Peptides ; toxicity ; Animals ; Animals, Newborn ; Cell Division ; drug effects ; Cells, Cultured ; Delayed Rectifier Potassium Channels ; Female ; Gene Expression ; drug effects ; Hippocampus ; cytology ; Male ; Neurons ; drug effects ; metabolism ; Peptide Fragments ; toxicity ; Potassium Channels ; biosynthesis ; genetics ; Potassium Channels, Voltage-Gated ; RNA, Messenger ; biosynthesis ; drug effects ; Rats ; Rats, Wistar ; Shab Potassium Channels

The relationship between the level of testosterone and the incidence of coronary heart disease is still controversial in the view of the results of clinical and epidemiologic studies. This uncertainty might be partly due to relatively small number of experimental studies undertaken to investigate the cellular mechanism underlying the vascular responses to testosterone. To further investigate the cellular mechanisms of testosterone with respect to vascular response, we investigated the effect of testosterone on contractility and intracellular Ca2+ regulation in a rabbit coronary artery and evaluated the underlying mechanism of testosterone-induced changes of coronary vascular tone by using various pharmacological blockers. Testosterone was found to relax rabbit coronary arteries in a dose-dependent manner, and no significant difference was found in the relaxation response to testosterone with or without endothelium. Similar results were obtained in male and non-pregnant female rabbit coronary arteries. The relaxation response of rabbit coronary arteries to testosterone was greater for PGF2alpha-contracted rings than for KCl contracted rings, which suggest the involvement of K+ channels. Furthermore, the relaxation response to testosterone was significantly reduced by 4-aminopyridine, a sensitive blocker of voltage dependent K+ channels, but not by low doses of tetraethylammonium or iberiotoxin, a Ca2+ activated K+ channel blocker. Testosterone simultaneously reduced the intracellular Ca2+ concentration ([Ca2+]i) and tension, and 4-AP effectively antagonized the testosterone-induced change of [Ca2+]i and tension. Therefore, it may be concluded that the stimulation of voltage dependent K channels is responsible, at least in part, for the testosterone-induced relaxation of rabbit coronary arteries.
Androgens/*pharmacology ; Animals ; Arteries/drug effects ; Calcium/*metabolism ; Coronary Vessels/*drug effects ; Female ; Intracellular Membranes/*metabolism ; Male ; Osmolar Concentration ; Potassium Channels, Voltage-Gated/drug effects/*metabolism ; Rabbits ; Support, Non-U.S. Gov't ; Testosterone/*pharmacology ; *Vasodilation

AIMTo study mRNA expression difference of voltage-dependent potassium channels in the brain of scopolamine-induced memory impaired rats.

METHODSMemory impairments induced in rats by scopolamine (1 mg.kg-1) were assessed in the Morris water maze test. After rats were injected intraperitoneally with scopolamine for 6 days, the mRNA expression level of five voltage-dependent potassium channels, Kv1.4, Kv1.5, Kv2.1, Kv4.2 and Kv4.3 were detected in the rat cortex and hippocampus by RT-PCR.

RESULTSScopolamine (1 mg.kg-1) was shown to significantly induce memory impairment in rats. The mRNA levels of Kv4.2 were decreased by 28.8% and 33.9% in the cortex and hippocampus, respectively. The mRNA levels of Kv1.4 and Kv2.1 were increased in the hippocampus by 111.7% and 64.3%, respectively. There were no differences in the brain mRNA levels of other voltage-dependent potassium channels in scopolamine-induced memory impaired rat.

CONCLUSIONThe mRNA expression levels of voltage-dependent potassium channels changed significantly in the brain of scopolamine-induced memory impaired rats.

Adjuvants, Anesthesia ; Animals ; Cerebral Cortex ; drug effects ; metabolism ; Hippocampus ; drug effects ; metabolism ; Male ; Maze Learning ; Memory Disorders ; chemically induced ; metabolism ; Potassium Channels, Voltage-Gated ; biosynthesis ; genetics ; RNA, Messenger ; biosynthesis ; Random Allocation ; Rats ; Rats, Wistar ; Scopolamine Hydrobromide

AIMTo investigat the effects of donepezil on delayed rectifier-like potassium currents (IK) in rat hippocampus and neocortex.

METHODSWhole cell configuration of the patch-clamp techniques were used to characterize IK in acutely isolated rat hippocampal and neocortical pyramidal neurons.

RESULTSThe slowly inactivating outward currents (IK) were recorded in all cells under investigation. Donepezil in micromolar concentrations were shown to supress the IK of all cells in a dose-dependent and voltage-dependent manner. The steady-state activation curves of IK were characterized by half-activation potentials of -15.5 mV in hippocampal and -4.1 mV in neocortical pyramidal neurons and were changed to -26.2 mV and -18.6 mV, respectively, after perfusion with donepezil (10 mumol.L-1).

CONCLUSIONAt concentrations as low as 1 mumol.L-1, donepezil was found to block the IK in a voltage-dependent manner in hippocampus and neocortex. This effect may be synergistic with the anticholinesterase activity of donepezil to increase its therapeutic effectiveness.

Animals ; Cholinesterase Inhibitors ; pharmacology ; Delayed Rectifier Potassium Channels ; Hippocampus ; cytology ; In Vitro Techniques ; Indans ; pharmacology ; Male ; Neocortex ; cytology ; Neurons ; drug effects ; metabolism ; Patch-Clamp Techniques ; Piperidines ; pharmacology ; Potassium Channels ; drug effects ; physiology ; Potassium Channels, Voltage-Gated ; Pyramidal Cells ; drug effects ; metabolism ; Rats ; Rats, Wistar

OBJECTIVETo study the inhibition of voltage-activated K(+) conductance and cell proliferation by 4-aminopyridine (4-AP) in the human small-cell lung cancer (SCLC).

METHODSInhibition of voltage-activated K(+) current by 4-AP through the whole-cell patch-clamp technique in SCLC cell line was studied. The influence on the cell-cycle by 4-AP was observed by flow cytometry to identify the in vitro inhibition by 4-AP to the cell proliferation of the SCLC cell line.

RESULTSExposure of the tumor cells to 5 mmol/L 4-AP reduced the peak outward K(+) current (evoked by a depolarization to +80 mV) from 1.22 +/- 0.11 nA (n = 30) to 0.59 +/- 0.10 nA (n = 28). Flow cytometry results showed that cell population accumulated in the G(0)/G(1) phase and a significantly reduced proportion in the S phase and G(1)/G(2) phase cells after having been exposed to 4-AP for three days. Incubation of the SCLC cells with 0.1, 5, 10, 15, 20 mmol/L 4-AP resulted in a concentration-and time-dependent reduction in the number of viable cells as compared with the control.

CONCLUSIONThe voltage-activated K(+) channels expressed by SCLC play an important role in SCLC cell proliferation. The proliferation of the SCLC cells is inhibited by K(+) channel antagonists.

4-Aminopyridine ; pharmacology ; Carcinoma, Small Cell ; pathology ; Cell Division ; drug effects ; Humans ; Lung Neoplasms ; pathology ; Potassium Channel Blockers ; pharmacology ; Potassium Channels, Voltage-Gated ; antagonists & inhibitors ; metabolism ; Tumor Cells, Cultured

AIMTo investigate the effects of blockers of the three kinds of potassium channels: voltage-dependent K+ channel(KV), calcium-activated K+ channel(KCa) and ATP-sensitive K+ channel(KATP), on the proliferation of rat bronchial smooth muscle cells (BSMCs).

METHODSThe effects of three kinds of potassium channel blockers on the proliferation of BSMCs were detected by MTT method, immunocytochemistry staining and flow-cytometry. Their effects on the dynamic changes of Ca2+ concentration in BSMCs were investigated by the fluorophotometry of Fura-2/AM.

RESULTSThe KV blocker 4-aminopyridine (4-AP) was shown to significantly increase the expression of proliferating cell nucleus antigen in cultured rat BSMCs (P < 0.01), but the KCa blocker tetraethylammonium (TEA) and KATP blocker glibenclamide(Glib) did not show such effect (P > 0.05). 4-AP was found to significantly increase the optical density value of the cultured BSMCs (P < 0.01) by MTT method and the numbers of S + G2M BSMCs(P < 0.05) by flow-cytometry. TEA and Glib did not show such effects. 4-AP significantly increased the Ca2+ concentration in cultured BSMCs(P < 0.01). TEA and Glib did not show such effects.

CONCLUSIONThis result suggests that inhibition of KV activity can increase intracellular Ca2+ and proliferation of rat BSMCs, but inhibition of KCa and KATP showed no effect.

4-Aminopyridine ; pharmacology ; Animals ; Bronchi ; cytology ; Calcium ; metabolism ; Cell Division ; drug effects ; Cells, Cultured ; Glyburide ; pharmacology ; Muscle, Smooth ; drug effects ; metabolism ; Potassium Channel Blockers ; pharmacology ; Potassium Channels, Calcium-Activated ; antagonists & inhibitors ; Potassium Channels, Voltage-Gated ; antagonists & inhibitors ; Proliferating Cell Nuclear Antigen ; metabolism ; Rats ; Rats, Sprague-Dawley ; Tetraethylammonium ; pharmacology

Hepatic stellate cells (HSCs) are known to play a role in the pathogenesis of the increased intrahepatic vascular resistance found in chronic liver diseases. The aim of this study was to evaluate the K+ and Ca2+ currents in cultured HSCs from rat liver, through the patch-clamp technique. Most cells were positive for desmin immunostain after isolation and in alpha-smooth muscle actin immunostain after 10 - 14 days of culturing. Outward and inward rectifying K+ currents were confirmed. Two different types of K+ currents were distinguished: one with the inward rectifying current and the other without. The outward K+ currents consisted of at least four components: tetraethylammonium (TEA) -sensitive current, 4-aminopyridine (4-AP) -sensitive current, pimozide-sensitive current and three blocker-resistant current. The peaks of the outward K+ currents evoked by a depolarizing pulse were decreased to 32.0 +/- 3.0, 62.8 +/- 3.7 and 32.8 +/- 3.5% by 5 mM TEA, 2 mM 4-AP and 15microM pimozide, respectively. Moreover, the combined application of three blockers caused 86.6 +/- 4.8% suppression. The inward currents evoked hyperpolarizing pulses were inwardly rectifying and almost blocked by Ba2+. Elevation of external K+ increased the inward current amplitude and positively shifted its reversal potential. Voltage- dependent Ca2+ currents which were completely abolished by Cd2+ and nimodipine were detected in 14 day cultured HSCs. In this study, the cultured HSCs were found to express outward K+ currents composed of multiple pharmacological components, Ba2+-sensitive inward rectifying K+ current and L-type Ca2+ current.
Animals ; Calcium/*metabolism ; Calcium Channel Blockers/pharmacology ; Calcium Channels, L-Type/*physiology ; Cells, Cultured ; Hepatocytes/cytology/*physiology ; Immunohistochemistry ; Male ; Membrane Potentials/drug effects/physiology ; Patch-Clamp Techniques ; Potassium/*metabolism ; Potassium Channel Blockers/pharmacology ; Potassium Channels, Voltage-Gated/*physiology ; Rats ; Rats, Sprague-Dawley