Akaike A, Mine Y, Sasa M, Takaori S
Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.
J Pharmacol Exp Ther. 1990 Oct;255(1):340-5.
A patch clamp study was performed to determine the ionic mechanisms underlying the muscarinic excitation of rat adrenal chromaffin cells. Burst-like, single-channel currents with brief openings were recorded during cell-attached or cell-free patch recording when the pipette solution contained high K+ media (70-140 mM), and the currents were recorded at potentials near the resting membrane potential. The amplitude and frequency of channel openings were dependent on the membrane potential and the K+ concentration of the external medium. Moreover, the single-channel currents observed with high K+ outside the membrane during inside-out recording were suppressed by the addition of a K+ channel blocker, tetraethylammonium, inside the membrane. These results suggest that the single K+ currents recorded in the present study had properties similar to those of the resting or muscarine-activated K+ currents in atrioventricular cells of the rabbit heart. During cell-attached patch recording with the high K+ medium in the recording pipette, muscarine at concentrations of 10(-5) to 10(-4) M dose dependently decreased the frequency of the channel openings but did not affect the current-voltage relationship or the time constants of open and close time histograms. These results indicate that muscarinic-induced suppression of K+ currents is caused by a decrease in the number of active K+ channels at the resting membrane potential.
进行了膜片钳研究以确定毒蕈碱对大鼠肾上腺嗜铬细胞兴奋作用的离子机制。当移液器溶液含有高钾培养基（70 - 140 mM）时，在细胞贴附或游离膜片记录过程中记录到了具有短暂开放的爆发样单通道电流，且这些电流是在接近静息膜电位的电位下记录的。通道开放的幅度和频率取决于膜电位和外部培养基中的钾离子浓度。此外，在膜外翻式记录中，当膜外为高钾时观察到的单通道电流，在膜内加入钾通道阻滞剂四乙铵后受到抑制。这些结果表明，本研究中记录的单钾电流具有与兔心脏房室细胞中静息或毒蕈碱激活的钾电流相似的特性。在用记录移液器中的高钾培养基进行细胞贴附膜片记录时，浓度为10^(-5)至10^(-4) M的毒蕈碱剂量依赖性地降低了通道开放的频率，但不影响电流 - 电压关系或开放和关闭时间直方图的时间常数。这些结果表明，毒蕈碱诱导的钾电流抑制是由静息膜电位下活性钾通道数量减少引起的。
