Dascal N, Snutch T P, Lübbert H, Davidson N, Lester H A
Science. 1986 Mar 7;231(4742):1147-50. doi: 10.1126/science.2418503.
Calcium ions flow into cells through several distinct classes of voltage-dependent calcium-selective channels. Such fluxes play important roles in electrical signaling at the cell membrane and in chemical signaling within cells. Further information about calcium channels was obtained by injecting RNA isolated from rat brain, heart and skeletal muscle into Xenopus oocytes. Macroscopic currents through voltage-operated calcium channels were resolved when the endogenous calcium-dependent chloride current was blocked by replacing external calcium with barium and chloride with methanesulfonate. The resulting barium current was insensitive to tetrodotoxin but was completely blocked by cadmium or cobalt. With both heart and brain RNA at least two distinct types of calcium ion conductance were found, distinguishable by their time course and inactivation properties. In oocytes injected with heart RNA, the slowly inactivating component was selectively blocked by the calcium-channel antagonist nifedipine. Barium ion currents induced by heart RNA were modulated by isoproterenol, cyclic adenosine monophosphate, and acetylcholine.
钙离子通过几种不同类型的电压依赖性钙选择性通道流入细胞。这种离子通量在细胞膜的电信号传导以及细胞内的化学信号传导中发挥着重要作用。通过将从大鼠脑、心脏和骨骼肌中分离出的RNA注射到非洲爪蟾卵母细胞中，获得了有关钙通道的更多信息。当用钡替代外部钙并用甲磺酸盐替代氯化物来阻断内源性钙依赖性氯化物电流时，可分辨出通过电压操作钙通道的宏观电流。由此产生的钡电流对河豚毒素不敏感，但被镉或钴完全阻断。在用心脏和脑RNA进行注射时，至少发现了两种不同类型的钙离子电导，可通过其时程和失活特性加以区分。在注射了心脏RNA的卵母细胞中，缓慢失活的成分被钙通道拮抗剂硝苯地平选择性阻断。由心脏RNA诱导的钡离子电流受到异丙肾上腺素、环磷酸腺苷和乙酰胆碱的调节。
