Ionic current study by patch clamp and its relation to the coronary artery spasm

采用膜片钳法对血管平滑肌细胞进行宏观电流记录。对豚鼠膀胱平滑肌细胞，去极化电压步骤引起初始向内电流后向外电流，对肠系膜动脉平滑肌细胞，去极化脉冲引起排他性向外电流。用110 mM Ba溶液代替移液管中的溶液，观察到血管平滑肌细胞向内流动。维拉帕米阻断了这种电流。这些结果表明，在正常情况下，血管平滑肌细胞不产生类钙，因为向外电流远大于向内电流。但是这些细胞确实有一个缓慢的向内电流，并且可能在某些异常情况下产生一个钙峰，在这种情况下，向外电流减少了。膜片钳对冠状动脉平滑肌细胞进行单通道记录，观察到许多具有不同电导的钙依赖性K通道，当钙离子进入细胞时，这些通道抑制了钙峰的形成。我们还发现了一个控制平滑肌细胞收缩的新的K通道。该通道依赖于外部Ca和/或Mg，被4-氨基吡啶阻断，并被尼可地尔和sit打开。随着K电流的减少，平滑肌细胞收缩。这些结果表明，K通道电流是控制动脉平滑肌细胞收缩的重要因素。

The loose patch clamp method was applied to the vascular smooth muscle cells to record their macroscopic current. With smooth muscle cells from the urinary bladder of guinea pigs, depolarizing voltage steps elicited and initial inward current followed by an outward current, while with smooth muscle cells of the mesenteric artery, depolarizing pulses elicited exclusively and outward current. On replacing the solution in the pipette by 110 mM Ba solution, an inward current was observed from the vascular smooth muscle cells. This current was blocked by verapamil. These results indicate that vascular smooth muscle cells do not produce a Ca-soike in normal conditions because the outward current is much larger than the inward current. But these cells do have a slow inward current and can presumably generate a Ca-spike in certain abnormal conditions, in which the outward current is decreased.In single channel recording of coronary artery smooth muscle cells by patch clamp, many Ca-dependent K channels with various conductance were observed, which inhibit developement of Ca-spike when Ca ion enters the cell. We also found a novel K channel which control contraction of the smooth muscle cells. This channel was dependent external Ca and/or Mg, blocked by 4-aminopyridine and opened by nicorandil and SITS. With decrease in this K current, smooth muscle cells contracts.These results suggest that K channel current is an important factor to control contraction of the smooth muscle cell of the artery.