Calcium channel activity in cultured embryonic hippocampal neurones was studied with the cell-attached configuration of the patch clamp technique. Single-channel recordings revealed the presence of a novel kind of calcium channel activity characterized by marked bursts of re-openings following voltage pulses to +20 mV from a holding potential of -40 mV. 2. The re-openings were greatly prolonged by the dihydropyridine (DHP) agonist (+)-(S)-202-791, thus ruling out the possibility that they arose from T-, N- or P-type channels. Furthermore, the novel gating pattern could be readily distinguished from that of the L-type channel which showed only conventional tail currents. 3. Since the novel gating pattern was stable over many minutes, we provisionally referred to it as a novel kind of calcium channel that showed voltage-dependent potentiation (Lp channel) to distinguish it from the 'standard' L-type channel (Ls channel). 4. Lp channels could also be distinguished from Ls channels on the basis of slope conductance (24.3 vs. 26.9 pS for Lp and Ls, respectively) and mean DHP-induced long open time (2.7 vs 11 ms at +20 mV for Lp and Ls, respectively). 5. Voltage-dependent potentiation of Lp channel activity was studied using a dual-pulse protocol. When preceded by conditioning prepulses, Lp responses to test pulses were greatly increased. Ls- and N-type calcium channels showed no such enhancement of their activity. 6. Long-duration recordings revealed no clear evidence for transitions from Ls to Lp gating (or vice versa), suggesting that Ls and Lp activities arose from different kinds of calcium channels or that Lp gating is an unusually long-lived mode of Ls channel gating.
摘要
采用膜片钳技术的细胞贴附式记录模式，对培养的胚胎海马神经元中的钙通道活性进行了研究。单通道记录显示存在一种新型钙通道活性，其特征是在从 -40 mV 的钳制电位向 +20 mV 进行电压脉冲后，会出现明显的再开放爆发。2. 二氢吡啶（DHP）激动剂（+）-（S）-202 - 791 可极大地延长再开放时间，从而排除了它们源于 T 型、N 型或 P 型通道的可能性。此外，这种新型门控模式很容易与仅显示传统尾电流的 L 型通道的门控模式区分开来。3. 由于这种新型门控模式在数分钟内保持稳定，我们暂时将其称为一种新型钙通道，该通道表现出电压依赖性增强作用（Lp 通道），以将其与“标准”L 型通道（Ls 通道）区分开来。4. Lp 通道在斜率电导方面（Lp 和 Ls 分别为 24.3 pS 和 26.9 pS）以及平均 DHP 诱导的长开放时间方面（在 +20 mV 时，Lp 和 Ls 分别为 2.7 ms 和 11 ms）也可与 Ls 通道区分开来。5. 使用双脉冲方案研究了 Lp 通道活性的电压依赖性增强作用。当在测试脉冲之前施加条件预脉冲时，Lp 对测试脉冲的反应会大大增强。Ls 型和 N 型钙通道未显示出这种活性增强。6. 长时间记录未发现从 Ls 门控转变为 Lp 门控（或反之亦然）的明确证据，这表明 Ls 和 Lp 活性源于不同类型的钙通道，或者 Lp 门控是 Ls 通道门控的一种异常长寿的模式。
