BACKGROUNDPrevious studies demonstrated general anesthetics affect potassium ion channels, which may be one of the mechanisms of general anesthesia. Because the effect of etomidate on potassium channels in rat hippocampus which is involved in memory function has not been studied, we investigated the effects of etomidate on both delayed rectifier potassium current (I(K(DR))) and transient outward potassium current (I(K(A))) in acutely dissociated rat hippocampal pyramidal neurons.

METHODSSingle rat hippocampal pyramidal neurons from male Wistar rats of - 10 days were acutely dissociated by enzymatic digestion and mechanical dispersion according to the methods of Kay and Wong with slight modification. Voltage-clamp recordings were performed in the whole-cell patch clamp configuration. Currents were recorded with a List EPC-10 amplifier and data were stored in a computer using Pulse 8.5. Student's paired two-tail t test was used for data analysis.

RESULTSAt the concentration of 100 micromol/L, etomidate significantly inhibited I(K(DR)) by 49.2% at +40 mV when depolarized from -110 mV (P < 0.01, n = 8), while did not affect I(K(A)) (n = 8, P > 0.05). The IC(50) value of etomidate for blocking I(K(DR)) was calculated as 5.4 micromol/L, with a Hill slope of 2.45. At the presence of 10 micromol/L etomidate, the V1/2 of activation curve was shifted from (17.3 +/- 1.5) mV to (10.7 +/- 2.9) mV (n = 8, P < 0.05), the V1/2 of inactivation curve was shifted from (-18.3 +/- 2.2) mV to (-45.3 +/- 9.4) mV (n = 8, P < 0.05). Etomidate 10 micromol/L shifted both the activation curve and inactivation curve of I(K(DR)) to negative potential, but mainly affected the inactivation kinetics.

CONCLUSIONSEtomidate potently inhibited I(K(DR)) but not I(K(A)) in rat hippocampal pyramidal neurons. I(K(DR)) was inhibited by etomidate in a concentration-dependent manner, while I(K(A)) remained unaffected.

Anesthetics, Intravenous ; pharmacology ; Animals ; Delayed Rectifier Potassium Channels ; drug effects ; physiology ; Etomidate ; pharmacology ; Male ; Potassium Channels ; drug effects ; physiology ; Pyramidal Cells ; drug effects ; physiology ; Rats ; Rats, Wistar

OBJECTIVETo study potassium currents in isolated Deiters' cells of guinea pig cochlea and explore possible function of potassium current in Deiters' cell.

METHODSThe whole cell patch clamp recording technique was used to study potassium currents of Deiters' cells in normal external solution and solutions with different K(+) concentrations. We also studied the effects on reversal potentials and outward potassium currents.

RESULTSIsolated Deiters' cells possess voltage dependent, outwardly rectifying ion channels, which are K(+) selective. 50 mmol/L K(+) and 150 mmol/L K(+) in external solution reduced I(K-max) from (10.06 +/- 2.2) nA (n = 13) in normal external solution to (6.43 +/- 1.67) nA (n = 6, P < 0.05) and (5.49 +/- 1.33) nA (n = 6, P < 0.05), respectively. While the amplitude of tailcurrents decreased from (468.76 +/- 61.76) pA in 5 mmol K(+) external solution to (224.74 +/- 35.89) pA (P < 0.05) in 50 mmol/L K(+) and to (-911.59 +/- 78.17) pA (P < 0.01) in 150 mmol/L K(+) external solution.

CONCLUSIONSOutwardly rectifying potassium in Deiters' cells could buffer extracellular K(+) in the small space between Deiters' cells and outer hair cells or neural fibers and participate in the diffusion of K(+) from endolymph to perilymph.

Animals ; Cochlea ; cytology ; drug effects ; physiology ; Dose-Response Relationship, Drug ; Guinea Pigs ; Membrane Potentials ; drug effects ; physiology ; Patch-Clamp Techniques ; Potassium ; pharmacology ; Potassium Channels ; physiology

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

OBJECTIVETo investigate the effect of diclofenac on the expression of Kv1.3 and Kir2.1 channels in human macrophages and the membrane potential and foaming process of the macrophages.

METHODSThe effect of diclofenac on the expression of Kv1.3 and Kir2.1 channels in cultured human monocyte-derived macrophages was investigated using real-time RT-PCR and Western blotting, and its effect on the membrane potential was analyzed with optical mapping of the membrane potential with voltage-sensitive dyes. The ratio of cholesterol ester (CE) in the macrophages following intake of oxidized low-density lipoprotein (OxLDL) was analyzed by an enzymatic fluorometric method.

RESULTSThe expression of Kv1.3 and Kir2.1 channels in the macrophages were down-regulated by diclofenac (1.5 µmol/L and 15 µmol/L). Compared with those in the control group, Kv1.3 mRNA expression was reduced by over 80% and 90% (P<0.05), and Kir2.1 mRNA by over 20% and 30% (P>0.05), respectively; both their protein expression was reduced by over 10% and 60% with a dose- dependent effect (P<0.05). Diclofenac at the two doses dose-dependently reduced the surface fluorescence intensity of the macrophage, and the membrane potential was decreased by 28% and 54%, respectively (P<0.05). Incubation of the macrophages with 30 mg/L OxLDL for 60 h caused an obvious enlargement of the cell volume and deposition of numerous lipid granules in cytoplasm, resulting also in a CE/TC ratio over 50% (P<0.05). Diclofenac at 1.5 and 15 µmol/L both significantly decreased the CE/TC ratio to (23.624∓3.34)% and (13.601∓2.916)% (P<0.05), respectively, but this effect did not show a dose-response relationship (P>0.05).

CONCLUSIONDiclofenac can significant down-regulate the expression of Kv1.3 and Kir2.1 channels in human macrophages, lower their membrane potential and inhibit the process of foam cell formation.

Cells, Cultured ; Diclofenac ; pharmacology ; Foam Cells ; cytology ; drug effects ; Humans ; Kv1.3 Potassium Channel ; metabolism ; Macrophages ; drug effects ; metabolism ; physiology ; Membrane Potentials ; drug effects ; Potassium Channels, Inwardly Rectifying ; metabolism

OBJECTIVETo understand what role of the transient outward potassium channels and the delayed rectifier potassium channels play in the mechanism of salicylate-induced tinnitus.

METHODSThe effects of salicylate on the transient outward potassium channels and the delayed rectifier potassium channels in freshly dissociated inferior colliculus neurons of rats were studied, using the whole-cell voltage clamp method.

RESULTSSalicylate blocked the transient outward potassium current (I(K(A and the delayed rectifier potassium current (I(K(DR in concentration-dependent manner (0.1-1 mmol/L). The IC50 values for the blocking action of salicylate on I(K(A)) and I(K(DR)) were 2.27 and 0.80 mmol/L, respectively. At a concentration of 1 mmol/L, salicylate did not shift the activation and inactivation curves of I(K(A)), but significantly shifted the activation and inactivation curves of I(K(DR)) negatively by approximately 11 mV and 24 mV.

CONCLUSIONSSalicylate inhibits both I(K(A)) and I(K(DR)) in rat inferior colliculus neurons but only significantly affects the activation and inactivation kinetics of I(K(DR)). Effects of I(K(A)) and I(K(DR)), especially I(K(DR)), by salicylate may play an important role in salicylate-induced tinnitus.

Animals ; Delayed Rectifier Potassium Channels ; drug effects ; Inferior Colliculi ; cytology ; drug effects ; Male ; Neurons ; drug effects ; physiology ; Patch-Clamp Techniques ; Potassium Channels ; drug effects ; physiology ; Rats ; Rats, Wistar ; Salicylates ; pharmacology

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

AIMThe effects of morphine on the potassium ionic currents of caudate nucleus neurons of neonatal rat were studied.

METHODSUsing of whole cell voltage clamp technique on caudate nucleus neurons, applied morphine chronically or acutely on it. In order to research the effects of morphine for voltage-gated of potassium ionic currents.

RESULTSThe amplitude of potassium ionic currents are increased by applied morphine acutely in caudate nucleus from (2.6 +/- 0.4) nA to (3.3 +/- 0.5) Na, naloxone can block the effect of morphine on K+ current and the currents are decreased to (2.4 +/- 0.4) nA. If applied morphine in caudate nucleus chronically, the amplitude of potassium ionic currents are increased from (2.6 +/- 0.4) nA to (3.1 +/- 0. 5) nA. After applied naloxone, the currents are decreased to (2.4 +/- 0.4) nA.

CONCLUSIONThe effects of morphine increased potassium ionic currents by micro-opioid receptor mediated and induced the hyper polarization of neurons, leading to inhibition of neural activity.

Animals ; Caudate Nucleus ; cytology ; drug effects ; physiology ; Morphine ; pharmacology ; Neurons ; drug effects ; physiology ; Patch-Clamp Techniques ; Potassium Channels ; drug effects ; physiology ; Rats ; Rats, Wistar

Action Potentials ; drug effects ; Angiotensin II Type 1 Receptor Blockers ; pharmacology ; Animals ; Biphenyl Compounds ; pharmacology ; Calcium Channels, L-Type ; drug effects ; physiology ; Heart Atria ; cytology ; drug effects ; Myocytes, Cardiac ; drug effects ; physiology ; Potassium Channels ; drug effects ; physiology ; Rabbits ; Tetrazoles ; pharmacology

To explore the underlying mechanism of acetylcholine (ACh)-evoked membrane hyperpolarizing response in isolated rat vas deferens smooth muscle cells (SMCs), intracellular microelectrode recording technique and intracellular microelectrophoresis fluorescent staining technique were used to study ACh-evoked membrane hyperpolarizing response in SMCs freshly isolated from Wistar rat vas deferens. By using microelectrodes containing fluorescent dye 0.1% propidium iodide (PI), 37 and 17 cells were identified as SMCs in outer longitudinal and inner circular muscular layers, respectively. The resting membrane potentials of SMCs were (-53.56+/-3.88) mV and (-51.62+/-4.27) mV, respectively. The membrane input resistances were (2245.60+/-372.50) MOmega and (2101.50+/-513.50) MOmega, respectively. ACh evoked membrane hyperpolarizing response in a concentration-dependent manner with an EC(50) of 36 micromol/L. This action of ACh was abolished by both a non-sepcific muscarinic (M) receptor antagonist atropine (1 mumol/L) and a selective M(3 ) receptor antagonist diphenylacetoxy-N-methylpiperidine-methiodide (DAMP, 100 nmol/L). ACh-evoked membrane hyperpolarization was also abolished by a nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME, 300 micromol/L) and suppressed by an ATP-sensitive potassium (K(ATP)) channel blocker glipizide (5 micromol/L) and an inward rectifier potassium (K(ir)) channel inhibitor bariumion (50 micromol/L). A combination of glipizide and bariumion abolished ACh-evoked membrane hyperpolarizing response. The results suggest that ACh-evoked membrane hyperpolarization in rat vas deferens SMCs is mediated by M(3) receptor followed with activation of K(ATP) channels, K(ir) channels, and NO release.
Acetylcholine ; pharmacology ; Animals ; Glipizide ; pharmacology ; In Vitro Techniques ; Male ; Membrane Potentials ; drug effects ; Myocytes, Smooth Muscle ; physiology ; Nitric Oxide ; physiology ; Potassium Channels ; physiology ; Potassium Channels, Inwardly Rectifying ; Rats ; Rats, Wistar ; Vas Deferens ; drug effects ; physiology

Adenosine ; pharmacology ; Animals ; Cyclic Nucleotide-Gated Cation Channels ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels ; Ion Channels ; physiology ; Isoproterenol ; pharmacology ; Membrane Potentials ; drug effects ; Muscle, Smooth, Vascular ; physiology ; Myocytes, Smooth Muscle ; physiology ; Potassium Channels ; Pulmonary Veins ; physiology ; Rabbits