Lacinová L, Hofmann F
Institut für Pharmakologie and Toxikologie TU München, Germany.
Recept Channels. 1998;6(3):153-64.
Triple mutation of Tyr1485, Met1486 and Ile1493 in the IVS6 segment of alpha 1C-b subunit of the L-type calcium channel results in a loss of the high affinity inhibition by isradipine. The mutant channel (Ch30) yet exhibits a concentration-dependent inhibition by isradipine with a 110-fold lower affinity. The mechanisms underlying the remaining low affinity block were investigated. Isradipine accelerated the current decay in Ch30 but not in wild type channel in a concentration dependent manner. Dependence of the current amplitude inhibition on holding potential was parallel in Ch30 and in wild type channels, while the acceleration of current decay in Ch30 was independent of the membrane potential. The recovery from voltage-dependent inactivation was biphasic in both channels and was slowed down by isradipine in the wild type but not in the Ch30 channel. The change of the charge carrier (Ba2+ or Ca2+) and calcium chelator (EGTA or BAPTA) did not affect the acceleration of current decay indicating that isradipine did not interact with the Ca(2+)-inactivated state of the channel. These results demonstrate that the mutations of Ch30 affect selectively the high affinity inhibition of an inactivated channel and unmask a low affinity interaction of isradipine with an open state of the channel.
L型钙通道α1C - b亚基IVS6片段中Tyr1485、Met1486和Ile1493的三重突变导致异搏定对其高亲和力抑制作用丧失。突变通道（Ch30）仍表现出异搏定浓度依赖性抑制作用，但其亲和力降低了110倍。对剩余低亲和力阻断的潜在机制进行了研究。异搏定以浓度依赖性方式加速Ch30中的电流衰减，但在野生型通道中则不然。Ch30和野生型通道中电流幅度抑制对钳制电位的依赖性是平行的，而Ch30中电流衰减的加速与膜电位无关。两个通道中电压依赖性失活的恢复都是双相的，异搏定在野生型通道中减缓了恢复过程，但在Ch30通道中则没有。电荷载体（Ba2+或Ca2+）和钙螯合剂（EGTA或BAPTA）的变化不影响电流衰减的加速，这表明异搏定不与通道的Ca(2+)失活状态相互作用。这些结果表明，Ch30的突变选择性地影响失活通道的高亲和力抑制，并揭示了异搏定与通道开放状态的低亲和力相互作用。
