肾上腺髓质瘤无性繁殖细胞的延时整流单钾离子通道

用片膜钳技术,在大鼠肾上腺髓质瘤无性繁殖细胞(PC12细胞)膜记录电压依赖性单钾离子通道活动:在细胞贴附式下去极化电流可激活一个电导为35～55皮西门(pS)的外向钾离子单通道。通道开放呈爆发型和快速闪动型,平均开放时间在0.5～20ms范围,其潜伏期随去极化程度增大而略变小。由撕开的膜片测得的翻转电位表明此通道选择性地让钾离于通过。通道在低钙(10 nmol/L自由钙离子)溶液中开放,增高胞浆侧钙离于浓度对通道开放无明显影响。20mmol/L四乙铵(TEA)可阻断该通道。在200ms的去极化脉冲中通道开放时间所占比例随去极化程度增大而增大,每20～30mV电位可使开放比率增高e(2.73)倍。在7～25秒长的去极化维持电位中,通道进入然后退出一个长时间的失活状态。以上结果表明,这类通道属于延时整流型钾通道。

A SINGLE DELAYED RECTIFIER POTASSIUM CHANNEL IN FHEOCHROMOCYTOMA(PCl2) CELLS

Single-channel recordings by using the gigaohm seal patch-clamp technique were carried out on the somatic membranes of clonal pheochromocytoma cells. In the cell-attached configuration, depolarizing voltage steps activated outward directed single-channel currents with conductance 35 to 55 pS. The channel openings exhibited bursting and flickering. The mean burst dwell durations ranges from 0.5 to 20 ms with a tendency to increase slightly at more depolarized voltage. Reversal potential measurements using excised membrane patches indicated that the channels behaved as a K -selective pore. Channel open in low (1-10nmol/L free) Ca2 solutions and increased the concentration of Ca2 in the cytoplasmic side did not influence the channel opening. It is blocked by 20mmol/L TEA. The fraction of time spent in the open state during the 200 ms depolarizing pulse increased e-folds for a 20 to 30 mV chanege in potential. During maintained depolarization step (7 to 25 second long), the channels enter and exit a long-live inactivative state. It is concluded that these channels belong to the class of delayed rectifier pottassium channels.