Satin L S, Cook D L
Department of Physiology, University of Washington, Seattle 98105.
Pflugers Arch. 1988 Apr;411(4):401-9. doi: 10.1007/BF00587719.
Inward currents were measured in cultured rat pancreatic islet cells using the whole-cell patch-clamp technique. Depolarization elicited both transient and more sustained inward currents. The transient current was blocked by external Na removal, TTX or depolarizing holding potentials while the sustained current was blocked by external Ca removal or the addition of Co, Ni or Cd ions to the external solution. Replacing Ca with Ba increased the amplitude of the sustained current and decreased its rate of decay. These results suggest that the transient current was due to the activation of Na channels while the sustained current was mediated by Ca channels. Two characteristics of the data suggested that two Ca currents may contribute to the sustained current. First, a second shoulder, or hump, was observed on the descending limb of the Ca current I-V of many cells, suggesting that they may possess two Ca channels that activate at different voltages. Second, the low and high voltage components of the I-V were differentially suppressed by Cd. Neither of the Ca current components was very sensitive to the Ca channel agonist BAY K 8644. These results were confirmed in HIT cells, another insulin-secreting preparation.
采用全细胞膜片钳技术在培养的大鼠胰岛细胞中测量内向电流。去极化引发了瞬时和更持续的内向电流。瞬时电流可被去除细胞外钠离子、使用河豚毒素（TTX）或去极化钳制电位所阻断，而持续电流可被去除细胞外钙离子或向细胞外溶液中添加钴、镍或镉离子所阻断。用钡离子替代钙离子可增加持续电流的幅度并降低其衰减速率。这些结果表明，瞬时电流是由于钠通道的激活，而持续电流是由钙通道介导的。数据的两个特征表明，两种钙电流可能对持续电流有贡献。首先，在许多细胞的钙电流I-V曲线的下降支上观察到第二个峰或隆起，这表明它们可能拥有两个在不同电压下激活的钙通道。其次，I-V曲线的低电压和高电压成分被镉离子不同程度地抑制。两种钙电流成分对钙通道激动剂BAY K 8644都不太敏感。这些结果在另一种胰岛素分泌制剂HIT细胞中得到了证实。
