We performed experiments using Aplysia neurons to identify the mechanism underlying the changes in the firing patterns in response to temperature changes. When the temperature was gradually increased from 11degrees C to 31degrees C the firing patterns changed sequentially from the silent state to beating, doublets, beating-chaos, bursting-chaos, square-wave bursting, and bursting-oscillation patterns. When the temperature was decreased over the same temperature range, these sequential changes in the firing patterns reappeared in reverse order. To simulate this entire range of spiking patterns we modified nonlinear differential equations that Chay and Lee made using temperature-dependent scaling factors. To refine the equations, we also analyzed the spike pattern changes in the presence of potassium channel blockers. Based on the solutions of these equations and potassium channel blocker experiments, we found that, as temperature increases, the maximum value of the potassium channel relaxation time constant, taun(t) increases, but the maximum value of the probabilities of openings for activation of the potassium channels, n(t) decreases. Accordingly, the voltage-dependent potassium current is likely to play a leading role in the temperature-dependent changes in the firing patterns in Aplysia neurons.
Aplysia ; Computer Simulation ; Fires ; Neurons ; Potassium ; Potassium Channel Blockers ; Potassium Channels ; Relaxation

Voltage-gated potassium channels (Kv4.1, Kv4.2 and Kv4.3) encoded by the members of the KCND/Kv4 (Shal) channel family mediate the native, fast inactivating (A-type) K(+) current (IA) described both in heart and neurons. This IA current is specifically blocked by short scorpion toxins that belong to the α-KTx15 subfamily and which act as pore blockers, a different mode of action by comparison to spider toxins known as gating modifiers. This review summarizes our present chemical and pharmacological knowledge on the α-KTx15 toxins.
Animals ; Potassium Channel Blockers ; chemistry ; Scorpion Venoms ; chemistry ; Scorpions ; Shal Potassium Channels ; antagonists & inhibitors

Potassium channel blockers slow depolarization, broaden the action potential, and thus pro- mote the open and inactivated Na+ channel states. The ability of local anesthetics to reduce the amplitude of compound action potential(CAP) of rat sciatic nerve was examined in the presence and absence of teteraethylammonium chloride(TEA) that selectively block K+ channels, In the presence of 1.3X10-5 M bupivacaine that inhibit the CAP by 22.5% at tonic stimulation, the addition of TEA(10-1M) increased this inhibition by another 27.5% and increased another 50% by phasic stimulation(20Hz). Also, dose response curve of bupivacaine in the presence of TEA(10-1M) showed marked shift to left of curve. The re- covery kinetics of bupivacaine in the presence of various coneentration of TEA(10-2-10-1M) showed marked delay of recovery(2X10-2 M), reocurrence of inhibition(90min,5X10-2 M), even no recovery(10-1M). TEA alone slightly depolarized the resting membrane which was represented as increment of CAP height from 0.9%(3min) to 12.3%(80min), and broadened mid-peak amplitude width by 2 times in 5X10-1M, 5.3 times in 1M. These experiments directly demonstrated that TEA potentiated the inhibition of CAP by bupivacaine and showed the poesibility of mixture of TEA and local anesthetics to potenti- ate impulse conduction blockade.
Action Potentials ; Anesthetics, Local ; Animals ; Bupivacaine* ; Kinetics ; Membranes ; Potassium Channel Blockers ; Rats ; Sciatic Nerve ; Tea ; Tetraethylammonium*

Voltage-dependent potassium channels (Kv) are involved in proliferation and transformation in mammary epithelial cells. In previous studies, several groups have detected various potassium channels in breast cancer cells, and they assumed that potassium channels are related to the development of breast carcinoma, although the precise mechanisms are still unknown. We have previously reported that 4-aminopyridine (4-AP), one kind of potassium channel (K(+) channel) blocker, could affect the proliferation of MCF10A cells. The aim of the present study is to explore the expression and properties of K(+) channels in human mammary epithelial cells (MCF10A) and whether Kv channels are required for the proliferation of MCF10A cell. Electrophysiological, MTT analysis, PCR and Western blot methods were used to identify a K(+) conductance which is involved in tumorigenesis and not yet be described in MCF10A cells. A voltage-dependent, outward rectification and 4-AP-sensitive K(+) current was observed in these cells. The perfusion of 5 mmol/L 4-AP significantly decreased the amplitude of Kv current from (912.5+/-0.6) pA to (275+/-0.8) pA (n=5, P<0.01), when cells were recorded using 800 ms voltage steps from a holding potential of -60 mV to voltage ranging from -60 mV to +60 mV. PCR analysis demonstrated that Kv1.1, Kv1.2, Kv1.3, and Kv1.5 were all expressed in MCF10A and MCF7 cells. Furthermore, the expression of Kv1.5 was much higher in MCF10A than that in MCF7. Inhibitory effect of 4-AP on cell proliferation was dosage-dependent. Incubation with 5 mmol/L 4-AP reduced MCF10A cell proliferation to 25.29% in 48 h. Western blot analysis showed the activation of ERK1/2 which related to cell proliferation was enhanced, while p38 activation was decreased by 4-AP treatment for 10 min. These data provided the first evidence of the Kv channels expression in MCF10A cell and 4-AP could inhibit the proliferation of MCF10A through blocking the potassium channels, and the mechanism may be related to regulating the activity of different members of cell proliferation signaling pathway of MEK/ERK.
4-Aminopyridine ; pharmacology ; Cell Line ; Cell Proliferation ; Epithelial Cells ; physiology ; Humans ; Potassium Channel Blockers ; pharmacology ; Potassium Channels, Voltage-Gated ; physiology

This study was designed to evaluate the effects of calcium and potassium channel blockers on local anesthetics-induced vascular relaxation of isolated rat thoracic aorta. In the presence of lidocaine and bupivacaine, the aortic rings previously contracted with phenylephrine(10(-4)M) were slightly contracted at the beginning of the administration of local anesthetics. But in the presence of tetracaine, aortic rings were not contracted at the beginnings. Verapamil, diltiazem and nifedipine in concentration of 10(-9)M to 10(-5)M produced cumulative concentration-dependent vasorelaxation significantly in the aortic rings previously contracted with phenylephrine(10(-4)M). In the presence of lidocaine, bupivacaine and tetracaine, verapamil, diltiazem and nifedipine in concentration of 10(-9)M to 10(-5)M caused dose-dependent vasorelaxation in aortic rings significantly. Tetraethylammonium HCl(TEA) in concentration of 10(-9)M to 10(-5)M did not produce dose-dependent vasorelaxation but slight contraction showed at the beginning of the administration. In the presence of lidocaine, bupivacaine, TEA in concentration of 10(-9)M to 10(-5)M did not produce vasorelaxation remarkably. But in the presence of tetracaine, TEA in concentration of 10(-9)M to 10(-5)M produced cumuIative concentration-dependent vasorelaxation significantly. These findings suggest that local anesthetics, especially tetracaine, which interact with calcium and potassium channel bleckers, lead to blockade of the sodium and calcium channels as well as potassium channels.
Anesthetics, Local ; Animals ; Aorta, Thoracic ; Bupivacaine ; Calcium Channel Blockers ; Calcium Channels ; Calcium* ; Diltiazem ; Lidocaine ; Nifedipine ; Potassium Channel Blockers* ; Potassium Channels* ; Potassium* ; Rats* ; Relaxation* ; Sodium ; Tea ; Tetracaine ; Tetraethylammonium ; Vasodilation ; Verapamil

AIMTo discover new regulators of potassium channel, an in vitro assay based on DiBAC4 (3) to determine the fluorescence was established for high throughput screening.

METHODSA cell-based 96-well format fluorescence assay using DiBAC4 (3) in cultured PC12 cells was described. Cells were loaded with 5 mumol.L-1 DiBAC4 (3) and incubated at 37 degrees C for 30 min before adding KCl or several known potassium channel regulators. The cellular DiBAC4 (3) fluorescence responce was then detected. The fluorescence changes can be used to evaluate membrane potential changes, which are determined mainly by potassium channels.

RESULTSExtracellular high K(+)-induced depolarization and several potassium channel blockers including 4-AP, TEA, E-4031, glibenclamide, quinidine and nifedipine all evoked increases in DiBAC4 (3) fluorescence response. The potassium channel opener, cromakalim, evoked decrease in DiBAC4 (3) fluorescence response. The fluorescence changes of 4-AP, TEA, glibenclamide, nifedipine and cromakalim were in a concentration-dependent manner. In 76 compounds screened by using the established DiBAC4 (3)-based assay, 9 compounds were found to change the fluorescence dose-dependently. Patch clamp technique is needed to further testify and screen their actions on potassium currents.

CONCLUSIONThe DiBAC4 (3)-based assay is easily operated, economical and repeatable. So, it can be performed by high throughput screening for potassium channel regulators.

4-Aminopyridine ; pharmacology ; Animals ; Barbiturates ; chemistry ; Calcium Channel Blockers ; pharmacology ; Cromakalim ; pharmacology ; Isoxazoles ; chemistry ; Membrane Potentials ; drug effects ; Nifedipine ; pharmacology ; PC12 Cells ; Patch-Clamp Techniques ; Piperidines ; pharmacology ; Potassium Channel Blockers ; pharmacology ; Potassium Channels ; drug effects ; Pyridines ; pharmacology ; Quinidine ; pharmacology ; Rats

BACKGROUND: The aim of the present study was to evaluate whether calcium channel blockers pretreatment increase blood potassium level after the administration of succinylcholine in hypertensive patients. METHODS: Eighty hypertensive patients were randomly divided into four groups: group I (saline, n = 20), group II (nicardipine 30 microg/kg, n = 20), group III (diltiazem 0.2 mg/kg, n = 20), group IV (verapamil 0.1 mg/kg, n = 20). The patients had been taking antihypertensive drugs regularly and their blood pressures were well controlled. Anesthesia was induced with thiopental sodium 5 mg/kg and tracheal intubation was facilitated with succinylcholine 1 mg/kg. Saline, nicardipine, diltiazem, and verapamil were administered two minutes before injection of succinylcholine in group I, II, III, and IV, respectively. Blood potassium level was measured prior to induction and 1, 3, 5, 10, 15, 30, 45, 60, 75, 90 minutes after administration of succinylcholine. RESULTS: Blood potassium levels at 5, 10, 15, and 30 minutes after the administration of succinylcholine were significantly increased compared with baseline values in all groups (P < 0.05). Blood potassium level was not different significantly among four groups at all times. CONCLUSIONS: Calcium channel blockers pretreatment did not increase blood potassium level after the administration of succinylcholine. We concluded that succinylcholine and calcium channel blocker can be used safely together in hypertensive patients.
Anesthesia ; Antihypertensive Agents ; Calcium ; Calcium Channel Blockers ; Calcium Channels ; Diltiazem ; Humans ; Intubation ; Nicardipine ; Potassium ; Succinylcholine ; Thiopental ; Verapamil

The effects of the antiarrhythmic drug propafenone at c-type kv1.4 channels in Xenopus laevis oocytes were studied with the two-electrode voltage-clamp techinique. Defolliculated oocytes (stage V-VI) were injected with transcribed cRNAs of ferret Kv1.4 delta N channels. During recording, oocytes were continuously perfused with control solution or propafenone. Propafenone decreased the currents during voltage steps. The block was voltage-, use-, and concentration- dependent manners. The block was increased with positive going potentials. The voltage dependence of block could be fitted with the sum of monoexponential and a linear function. Propafenone accelerated the inactivate of current during the voltage step. The concentration of half-maximal block (IC(50)) was 121 micrometer/L. With high, normal, and low extracellular potassium concentrations, the changes of IC(50) value had no significant statistical differences. The block of propafenone was PH- dependent in high-, normal- and low- extracellular potassium concentrations. Acidification of the extracellular solution to PH 6.0 increased the IC50 values to 463 micrometer/L, alkalization to PH 8.0 reduced it to 58 micrometer/L. The results suggest that propafenone blocks the kv1.4 delta N channel in the open state and give some hints for an intracellular site of action.
Animals ; Anti-Arrhythmia Agents/*pharmacology ; Hydrogen-Ion Concentration ; Inhibitory Concentration 50 ; Kv1.4 Potassium Channel/*antagonists & inhibitors/metabolism ; Oocytes/drug effects/metabolism ; Patch-Clamp Techniques ; Potassium/*metabolism ; Potassium Channel Blockers/*pharmacology ; Propafenone/*pharmacology ; Xenopus laevis

PURPOSE: Ion channels play key roles in determining smooth muscle tone by setting the membrane potential and allowing Ca2+ influx. Potassium channels may be important in modulating corporal smooth muscle tone. In this study, we investigated the effects of potassium channels in the rabbit corpus cavernosal smooth muscle by blocking them with various agents. MATERIALS AND METHODS: Strips of rabbit corpus cavernosum were prepared for mounting and isometric tension measurement in an organ bath. On cavernosal strips contracted with phenylephrine (PHE), sodium nitroprusside (SNP) was applied in increasing concentrations from 10(-7)M to 10(-4)M, causing dose-dependent relaxation. The effects of various potassium channel blockers on SNP-induced relaxation were then evaluated by measuring the tension of the cavernosal strips. The potassium channel blockers used were tetraethyl ammonium (TEA), charybdotoxin, gliben clamide, and apamin. RESULTS: The relaxation responses to SNP of the corporal preparations contracted in response to PHE were significantly attenuated by TEA (10(-2)M) and charybdotoxin (10(-7)M), with no significant difference observed between the two drugs. The SNP-induced relaxation responses were not significantly attenuated by glibenclamide (10(-5)M) or apamin (10(-5)M). CONCLUSIONS: These results suggest that maxi-K+ channels play an important role in corpus cavernosal relaxation. The KATP channel and small-conductance KCa channel are thought to be unrelated to corpus cavernosal smooth muscle relaxation.
Ammonium Compounds ; Apamin ; Baths ; Charybdotoxin ; Glyburide ; Ion Channels ; Membrane Potentials ; Muscle, Smooth ; Nitric Oxide ; Nitroprusside ; Phenylephrine ; Potassium Channel Blockers ; Potassium Channels ; Relaxation* ; Tea

OBJECTIVETo investigate the effect of midazolam on human ether-a-go-go (hERG) K+ channels exogenously expressed in human embryonic kidney cells (HEK-293) and the underlying molecular mechanisms.

METHODSWhole-cell patch clamp technique was used to record WT, Y652A and F656C hERG K+ current expressed in HEK-293 cells.

RESULTSMidazolam inhibited hERG K+ current in a concentration-dependent manner, the half-maximum block concentrations (IC50) values were (1.31 ± 0.32) µmol/L. The half-activation voltage (V1/2) were (2.32 ± 0.38) mV for the control and (-1.96 ± 0.83) mV for 1.0 µmol/L midazolam. The half-inactivation voltage (V1/2) was slightly shifted towards negative voltages from (-49.25 ± 0.69) mV in control to (-57.53 ± 0.53) mV after 1.0 µmol/L midazolam (P < 0.05). Mutations in drug-binding sites (Y652A or F656C) of the hERG channel significantly attenuated the hERG current blockade by midazolam.

CONCLUSIONMidazolam can block hERG K+ channel and cause the speed of inactivation faster. Mutations in the drug-binding sites (Y652 or F656) of the hERG channel were found to attenuate hERG current blockage by midazolam.

Dose-Response Relationship, Drug ; Ether-A-Go-Go Potassium Channels ; drug effects ; HEK293 Cells ; Humans ; Midazolam ; pharmacology ; Mutation ; Patch-Clamp Techniques ; Potassium Channel Blockers ; pharmacology