Deiters' cells are the supporting cells in organ of Corti and are suggested to play an important role in biochemical and mechanical modulation of outer hair cells. We successfully isolated functionally different K+ currents from Deiters' cells of guinea pig using whole cell patch clamp technique. With high K+ pipette solution, depolarizing step pulses activated strongly outward rectifying currents which were dose-dependently blocked by clofilium, a class III anti-arrhythmic K+ channel blocker. The remaining outward current was transient in time course whereas the clofilium-sensitive outward current showed slow inactivation and delayed rectification. Addition of 5 mM tetraethylammonium (TEA) further blocked the remaining current leaving a very fast inactivating transient outward current. Therefore, at least three different types of K+ current were identified in Deiters' cells, such as fast activating and fast inactivating current, fast activating slow inactivating current, and very fast inactivating transient outward current. Physiological role of them needs to be established.
Animals ; Ear, Inner ; Guinea Pigs* ; Guinea* ; Hair ; Hearing ; Organ of Corti ; Pharmacology ; Potassium Channels ; Potassium* ; Quaternary Ammonium Compounds ; Tetraethylammonium

Isolated rabbit aortic ring with intact endothelial cell preparations precontracted with NE (10(-7) M) were relaxed by vanadate in a dose dependent manner (from 0.2 to 2 mM). Application of vanadate and ACh during the tonic phase of high K+(100 mM)-induced contraction showed a slight relaxation in contrast to that in NE-induced contraction, but sodium nitroprusside (10 microM) more effectively relaxed the aortic ring preparations in high K+ contraction than that of vanadate. Vanadate-induced relaxation in NE-contracted aortic rings was reversed by application of BaCl2 (50 microM) or glibenclamide (10 microM). Furthermore, Vanadate hyperpolarized membrane potential of smooth muscle cells in endothelium-intact aortic strips and this effect was abolished by application of glibenclamide. The above results suggest that vanadate release EDHF (Endothelium-Derived Hyperpolarizing Factor), in addition to EDRF (Endothelium-Derived Relaxing Factor) from endothelial cell. This EDHF hyperpolarize the smooth muscle cell membrane potential via opening of the ATP-sensitive K+ channel and close a voltage dependent Ca++ channel. So it is suggested that the vanadate-induced relaxation of rabbit thoracic aortic rings may be due to the combined effects of EDRF and EDHF.
Animal ; Aorta/drug effects/physiology ; In Vitro ; Membrane Potentials/drug effects ; Potassium/pharmacology ; Potassium Channels/physiology ; Rabbits ; Support, Non-U.S. Gov't ; Tetraethylammonium Compounds/pharmacology ; Vanadates/*pharmacology ; Vasodilation/*drug effects

In this paper, membrane current properties of the fully-grown oocytes from toad, Bufo bufo gargarizans, were studied by using two-microelectrode voltage clamp technique. Axion of adult female toad was destroyed, and then ovarian lobes containing oocytes in stage I to VI were removed and incubated in Ca(2+)-free ND96 solution with collagenase (1.5 mg/ml) for 1 h. Subsequently, the oocytes were washed in Ca(2+)-free ND96 solution for 10 min to completely remove the follicular layer. For the experiments only the oocytes in stage V and VI were selected and used during 1 to 5 d. The membrane was depolarized from a holding potential of -80 mV to +60 mV in 10 mV step. It was found that a sustained outward current was elicited by depolarization. Potassium channel blockers (tetraethylammonium chloride, TEA, 10 mmol/L and 4-aminopyridine, 4-AP, 10 mmol/L) reduced the outward current to (23.4+/-0.72)% of the maximum. However, further addition of chloride channel blocker (5-nitro-2, 3-phenypropylamino benzoate, NPPB, 30 micromol/L) could almost completely block the outward current to (2.1+/-0.08)% of the maximum. In the presence of TEA and 4-AP, removal of extracellular Ca(2+) or adding verapamil (40 micromol/L), could also reduce the outward current to (2.2+/-0.04) % and (3.1+/-0.15) % of the maximum, respectively. It is concluded that calcium-dependent chloride channels exist in plasma membrane of Bufo bufo gargarizans oocytes, besides potassium channels.
4-Aminopyridine ; toxicity ; Animals ; Bufo bufo ; Calcium ; metabolism ; Cell Membrane ; metabolism ; Chloride Channels ; drug effects ; physiology ; Female ; Nitrobenzoates ; pharmacology ; Oocytes ; metabolism ; Tetraethylammonium Compounds ; pharmacology ; Verapamil ; pharmacology

OBJECTIVETo study the effect of nitric oxide-induced tyrosine phosphorylation of large-conductance calcium-activated potassium (BK(Ca)) channel alpha subunit on vascular hyporesponsiveness in rats.

METHODSA total of 46 Wistar rats of either sex, weighing 250 g +/- 20 g, were used in this study. Models of vascular hyporesponsiveness induced by hemorrhagic shock (30 mm Hg for 2 hours) in vivo and by L-arginine in vitro were established respectively. The vascular responsiveness of isolated superior mesenteric arteries to norepinephrine was observed. Tyrosine phosphorylation of BK(Ca) alpha subunit was evaluated with methods of immunoprecipitation and Western blotting.

RESULTSIn the smooth muscle cells of the superior mesenteric arteries, the expression of BK(Ca) alpha subunit tyrosine phosphorylation increased following hemorrhagic shock, and L-arginine could induce BK(Ca )channel alpha subunit tyrosine phosphorylation in a time- and dose-dependent manner. L-NAME (Nomega-nitro-L-arginine-methyl-ester), a nitric oxide synthetase inhibitor, could partly restore the decreased vasoresponsiveness of the superior mesenteric arteries after hemorrhagic shock in rats. Down-regulating the protein tyrosine phosphorylation with genistein, a widely-used special protein tyrosine kinase inhibitor, could partly improve the decreased vasoresponsiveness of the superior mesenteric arteries induced by L-arginine in vitro, while up-regulating the protein tyrosine phosphorylation with Na(3)VO(4), a protein tyrosine phosphatase inhibitor, could further decrease the nitric oxide-induced vascular hyporesponsiveness, which could be partly ameliorated by 0.1 mmol/L tetrabutylammonium chloride (TEA), a selective BK(Ca )inhibitor at this concentration.

CONCLUSIONSNitric oxide can induce the tyrosine phosphorylation of BK(Ca) alpha subunit, which influences the vascular hyporesponsiveness in hemorrhagic shock rats or induced by L-arginine in vitro.

Animals ; Arginine ; pharmacology ; Cells, Cultured ; Female ; Male ; Mesenteric Artery, Superior ; drug effects ; physiopathology ; Nitric Oxide ; physiology ; Phosphorylation ; Potassium Channels, Calcium-Activated ; metabolism ; Protein Subunits ; Rats ; Rats, Wistar ; Shock, Hemorrhagic ; metabolism ; Tetraethylammonium Compounds ; pharmacology ; Tyrosine ; metabolism ; Vasoconstriction ; drug effects

This study was designed to identify and characterize Na+ -activated K+ current (I(K(Na))) in guinea pig gastric myocytes under whole-cell patch clamp. After whole-cell configuration was established under 110 mM intracellular Na+ concentration ([Na+]i) at holding potential of -60 mV, a large inward current was produced by external 60 mM K+([K+] degree). This inward current was not affected by removal of external Ca2+. K+ channel blockers had little effects on the current (p>0.05). Only TEA (5 mM) inhibited steady-state current to 68+/-2.7% of the control (p<0.05). In the presence of K+ channel blocker cocktail (mixture of Ba2+, glibenclamide, 4-AP, apamin, quinidine and TEA), a large inward current was activated. However, the amplitude of the steadystate current produced under [K+]degree (140 mM) was significantly smaller when Na+ in pipette solution was replaced with K+ - and Li+ in the presence of K+ channel blocker cocktail than under 110 mM [Na+]i. In the presence of K+ channel blocker cocktail under low Cl- pipette solution, this current was still activated and seemed K+ -selective, since reversal potentials (E(rev)) of various concentrations of [K+]degree-induced current in current/voltage (I/V) relationship were nearly identical to expected values. R-56865 (10-20 microgram), a blocker of IK(Na), completely and reversibly inhibited this current. The characteristics of the current coincide with those of IK(Na) of other cells. Our results indicate the presence of IK(Na) in guinea pig gastric myocytes.
Tetraethylammonium Compounds/pharmacology ; Stomach/*physiology ; Sodium/metabolism/*pharmacology ; Potassium Channels/*physiology ; Potassium Channel Blockers/pharmacology ; Myocytes, Smooth Muscle/*physiology ; Membrane Potentials ; Male ; Guinea Pigs ; Female ; Chlorides/pharmacology ; Calcium/metabolism ; Animals

OBJECTIVETo study the effects of resvaratrol derivatives on spontaneous HR and CF of isolated guinea pig atrium.

METHODThe dose-effect curve of resvaratrol was observed. The possible mechanism of potassium channels responsible for changes of CF and HR after administering with resvaratrol was measured.

RESULTResvaratrol reduced the spontaneous HR and weakened the CF in a dose-dependent manner ranging from 10(-6) to 3 x 10(-4) mol x L(-1) (P < 0.05). As compared with Res group, the effects were partly blocked by Gli (P < 0.05) and TEA (P < 0.01), but not blocked by 4-AP, BaCl2, Atropine.

CONCLUSIONResvaratrol can induce negative chronotropic action and negative (inotropic action. The mechanism(s) may relate to the opening of K(ATP) and Kc(Ca).

Animals ; Barium Compounds ; pharmacology ; Cardiotonic Agents ; administration & dosage ; isolation & purification ; pharmacology ; Chlorides ; pharmacology ; Dose-Response Relationship, Drug ; Female ; Glyburide ; pharmacology ; Guinea Pigs ; Heart Rate ; drug effects ; In Vitro Techniques ; KATP Channels ; antagonists & inhibitors ; Male ; Myocardial Contraction ; drug effects ; Plants, Medicinal ; chemistry ; Potassium Channel Blockers ; pharmacology ; Potassium Channels, Calcium-Activated ; antagonists & inhibitors ; Potassium Channels, Inwardly Rectifying ; antagonists & inhibitors ; Stilbenes ; administration & dosage ; isolation & purification ; pharmacology ; Tetraethylammonium ; pharmacology

BACKGROUND: Recently, the phannacologic and therapeutic significance of various types of potassium channels are being realized. Thus it was attempted to delineate the role of voltage-gated K+ -channels on the excitation-contraction coupling in skeletal muscle. METHODS: The effects of tetraethylammonium, a well known K+ -channel blocker, on the electrically-evoked twitch response, train-of-four and tetanic stimulation, and the influence of various agents on the these effects were studied in the isolated rat hemi-diaphragm preparation. RESULTS: Tetraethylammonium (1 & 3 mM) increased the electrically-evoked twitch response, but the large dose (10 mM) decreased the twitch response. And tetraethylammonium decreased the TOF- and tetanus-ratio in a dose-related fashion. d-Tubocurarine(1 microM) decreased the twitch response, and tetraethylammonium recovered the d-tubocurarine-induced-depression of twitch response. When the Ca++(6x) and K+ (2x) concentration of the medium were increased, the twitch response caused by tetraethylammonium were slightly inhibited than that observed in the normal solution, but the fade phenomenon was potentiated. The tetraethylammonium (10 mM)-induced depression of twitch response were reduced by reducing the stimulus frequency to 0.01 Hz and choline (400 microM) treatment. And N-ethylmaleimide inhibited the tetraethylammonium-induced increment of twitch response and also potentiated the tetraethylammonium-induced fade phenomenon. However, it is noteworth the 4-aminopy- ridine, another K+ -channel bloker, potentiated the electrically-evoked twitch response but did not affect the TOF-and tetanusratio. CONCLUSION: These result indicate that tetraethylammonium elicited two districtive types of response in the rat phrenic-hemidiaphragm preparation. The potentiating effects of twitch response is mediated by blocking delayed K+ -rectifier channel and decreasing effects of twitch response, TOF-and tetanus-ratio is may be due to decreased the acetylcholine release from presynaptic nerve terminal.
Acetylcholine ; Animals ; Choline ; Depression ; Ethylmaleimide ; Muscle, Skeletal ; Potassium Channels ; Rats* ; Tetraethylammonium*

BACKGROUND: This study investigated the effects of the K+ channel opener, pinacidil on hypoxic pulmonary vasoconstriction in isolated perfused rabbit lungs. In order to evaluate the vasodilatation mechanism of K+ channel opener, we also studied the effects of two K+ channel blocker, tetraethylammonium (TEA), a Ca2+ activated K+ channel blocker and glibenclamide (GLB), an ATP-sensitive K+ channel blocker. METHODS: Isolated lungs from white rabbits were ventilated with a normoxic gas (21%O2-5%CO2-74%N2) and a hypoxic gas (3%O2- 5%CO2-92%N2) alternatively, and then perfused with blood-containing perfusate solution. After a hypoxic pressor response (HPR) had been obtained, various drugs were added to the perfusate reservoir to achieve the predetermined circulating concentration, and the influences of the drugs on HPR were then tested. RESULTS: Pinacidil (0.3-6.0 mcM) produced a dose-dependent pulmonary vasodilation on hypoxic ventilation challenge. TEA (1 mM) caused pulmonary vasoconstriction in normoxic ventilation and potentiated a hypoxic pressor response. When the hypoxic pressor response was potentiated by TEA, pinacidil (1.0, 3.0 mcM) reduced the contraction, but GLB did not cause pulmonary vasoconstriction under normoxic ventilation, potentiate a hypoxic pressor response. CONCLUSIONS: Piacidil is capable of opposing the pulmonary responses of acute hypoxia. Moreover the effects of TEA and GLB suggest that HPV might be mediated through Ca2+ activated K+ channels, not through ATP-sensitive K+ channels.
Anoxia ; Glyburide* ; Lung* ; Pinacidil* ; Potassium Channels, Calcium-Activated ; Rabbits ; Tea ; Tetraethylammonium ; Vasoconstriction* ; Vasodilation ; Ventilation

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*

The profile of membrane currents was investigated in differentiated neuronal cells derived from human neural stem cells (hNSCs) that were obtained from aborted fetal cortex. Whole-cell voltage clamp recording revealed at least 4 different currents: a tetrodotoxin (TTX)-sensitive Na+ current, a hyperpolarization-activated inward current, and A-type and delayed rectifier-type K+ outward currents. Both types of K+ outward currents were blocked by either 5 mM tetraethylammonium (TEA) or 5 mM 4-aminopyridine (4-AP). The hyperpolarization-activated current resembled the classical K+ inward current in that it exhibited a voltage-dependent block in the presence of external Ba2+ (30micrometer) or Cs+ (3micrometer). However, the reversal potentials did not match well with the predicted K+ equilibrium potentials, suggesting that it was not a classical K+ inward rectifier current. The other Na+ inward current resembled the classical Na+ current observed in pharmacological studies. The expression of these channels may contribute to generation and repolarization of action potential and might be regarded as functional markers for hNSCs-derived neurons.
4-Aminopyridine ; Action Potentials ; Humans ; Membranes ; Neural Stem Cells ; Neurons ; Tetraethylammonium ; Tetrodotoxin