氟烷和异氟烷降低犬脑动脉肌细胞中钾离子通道的开放状态概率。

Eskinder H, Gebremedhin D, Lee J G, Rusch N J, Supan F D, Kampine J P, Bosnjak Z J

Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226.

Anesthesiology. 1995 Feb;82(2):479-90. doi: 10.1097/00000542-199502000-00018.

BACKGROUND

Both halothane and isoflurane evoke cerebral vasodilation. One of the potential mechanisms for arterial vasodilation is enhanced K+ efflux resulting from an increased opening frequency of membrane K+ channels. The current study was designed to determine the effects of volatile anesthetics on K+ channel current in single vascular smooth muscle cells isolated from dog cerebral arteries.

METHODS

Patch clamp recording techniques were used to investigate the effects of volatile anesthetics on macroscopic and microscopic K+ channel currents.

RESULTS

In the whole-cell patch-clamp mode, in cells dialyzed with pipette solution containing 2.5 mM EGTA and 1.8 mM CaCl2, depolarizing pulses from -60 to +60 mV elicited an outward K+ current that was blocked 65 +/- 5% by 3 mM tetraethylammonium (TEA). Halothane (0.4 and 0.9 mM) depressed the amplitude of this current by 18 +/- 4% and 34 +/- 6%, respectively. When 10 mM EGTA was used in the pipette solution to strongly buffer intracellular free Ca2+, an outward K+ current insensitive to 3 mM TEA was elicited. This K+ current, which was reduced 51 +/- 4% by 1 mM 4-aminopyridine, was also depressed by 17 +/- 5% and 29 +/- 7% with application of 0.4 and 0.9 mM halothane, respectively. In cell-attached patches using 145 mM KCl in the pipette solution and 5.2 mM KCl in the bath, the unitary conductance of the predominant channel type detected was 99 pS. External application of TEA (0.1 to 3 mM) reduced the unitary current amplitude of the 99 pS K+ channel in a concentration-dependent manner. The open state probability of this 99 pS K+ channel was increased by 1 microM Ca2+ ionophore (A23187). These findings indicate that the 99 pS channel measured in cell-attached patches was a TEA-sensitive, Ca(2+)-activated K+ channel. Halothane and isoflurane reversibly decreased the open state probability (NPo), mean open time, and frequency of opening of this 99 pS K+ channel without affecting single channel amplitude or the slope of the current-voltage relationship.

CONCLUSIONS

Halothane and isoflurane suppress the activity of K+ channels in canine cerebral arterial cells. These results suggest that mechanisms other than K+ channel opening likely mediate volatile anesthetic-induced vasodilation.

背景

氟烷和异氟烷均可引起脑血管舒张。动脉血管舒张的一种潜在机制是膜钾通道开放频率增加导致钾离子外流增强。本研究旨在确定挥发性麻醉剂对从犬脑动脉分离的单个血管平滑肌细胞钾通道电流的影响。

方法

采用膜片钳记录技术研究挥发性麻醉剂对宏观和微观钾通道电流的影响。

结果

在全细胞膜片钳模式下，用含2.5 mM乙二醇双四乙酸（EGTA）和1.8 mM氯化钙（CaCl2）的吸管溶液透析细胞时，从-60 mV到+60 mV的去极化脉冲引发外向钾电流，该电流被3 mM四乙铵（TEA）阻断65±5%。氟烷（0.4 mM和0.9 mM）分别使该电流幅度降低18±4%和34±6%。当吸管溶液中使用10 mM EGTA来强力缓冲细胞内游离钙离子时，引发了对3 mM TEA不敏感的外向钾电流。该钾电流被1 mM 4-氨基吡啶降低51±4%，在应用0.4 mM和0.9 mM氟烷时也分别降低17±5%和29±7%。在吸管溶液中使用145 mM氯化钾且浴槽中使用5.2 mM氯化钾的细胞贴附膜片中，检测到的主要通道类型的单位电导为99 pS。外部应用TEA（0.1至3 mM）以浓度依赖方式降低99 pS钾通道的单位电流幅度。1 μM钙离子载体（A23187）增加了该99 pS钾通道的开放状态概率。这些发现表明，在细胞贴附膜片中测量的99 pS通道是一种TEA敏感的、钙激活的钾通道。氟烷和异氟烷可逆地降低该99 pS钾通道的开放状态概率（NPo）、平均开放时间和开放频率，而不影响单通道幅度或电流-电压关系的斜率。