原代培养猪冠状动脉平滑肌的电压依赖和钙激活钾通道

目的：研究原代培养的猪冠状动脉平滑肌电压依赖性和钙激活外向钾通道的特性。方法：离子通道电流采用膜片钳技术进行记录。结果：在内面向外式膜片构型，当膜内外K^ 浓度梯度类似生理状态时，该通道单位电导值约为100pS，而当膜内外K^ 浓度为对称的140mM浓度时，该通道单位电导值约270pS。其平均电流显示该通道具时间和电压依赖性激活特性，而无任何时间和电压依赖性失活特性。另外，通道的开放时间常数和开放概率随除极及胞内Ca^2 的增加而显著增加。通过用EGTA降低胞浆内Ca^2 浓度，可使外向电流抑制。动力学分析显示通道激活时存在一种开放状态和至少两种关闭状态。四乙胺（TEA）可在胞外侧阻断该电流，但高达15mM的4－氨基吡啶（4－AP）在胞内外都对通道无影响。在全细胞构型，对细胞膜进行除极可引出宏观外向电流。随着细胞的除极，该电流的激活时间常数逐渐缩短，并显示快速激活动力学特性。结论：在原代培养的猪冠状动脉平滑肌上存在有电压依赖和Ca^2 激活的K^ 选择性离子通道。该类通道具有非常高的单位电导值，除极时快速开放，对胞内Ca^2 高度敏感，但无失活等特性。

VOLTAGE- DEPENDENT AND Ca2+ - ACTIVATED POTASSIUM CHANNEL IN PRIMARY CULTURED SMOOTH MUSCLE CELLS FROM PORCINE CORONARY ARTERY

Objective: To study the characteristics of the voltage-dependent and Ca 2+ -activated outward K + channel in primary cultured smooth muscle cells of porcine coronary artery. Method:The channel currents were recorded using the patch-clamp technique. Results:In inside-out patch configurations, The K + channel had a single-channel unitary conductance of about 100 pS in quasiphysiological K + gradients and about 270 pS with symmertricai 140mM K + solution.The averaged current showed a time-and voltage-dependent activation, but did not show any time-and voltage-dependent intctivation.Furthermore, the open time constants and the open probability of the channel were markedly increased not only with depolarization but also with elevation of [Ca 2+ ] i,and the outward currents were inhibited by lowering cystosolic Ca 2+ with EGTA.Kinetics analysis showed the presence of one open state and at least two closed states for the channel activity. Tetraethylammonium (TEA) abolished the outward current at external surface of membrane, but 4-aminopyridine(4-AP)had on effect at concentration up to 15 mM in each side of membrane. In whole-cell voltage-clamp configurations, the macroscopic outward currents were elicited from cell depolarization. The activition time constant was gradually shortened with membrane depolarization and reveals a fast activation kinetics. Conclusion:A population of vlotage-dependent and Ca 2+ -activited K +-selective ion channel exists in primary cultured smooth muscle cells of porcine coronary artery which is characterized by a very high unitary conductance, a fast open kinetics upon depolarization, and highly sensitivity to [Ca 2+ ] i,but without inactivation.