In smooth muscle cells enzymatically isolated from guinea-pig urinary bladder, Ca2+ channel currents were recorded by conventional cell-attached patch clamp techniques. In most recordings Bay K 8644 (2 microM) was contained in the patch pipette. 2. Closure of Ca2+ channels observed during the repolarizing steps was significantly slowed by preconditioning with large depolarizations (+80 and 100 mV), with or without Bay K 8644 in the pipette. 3. The sum of the unitary Ca2+ channel current traces obtained after large conditioning depolarizations (in the presence of Bay K 8644) showed a slowly deactivating tail current. 4. By use of this slow deactivating feature, the current-voltage relationship of the unitary Ca2+ channel current was continuously measured with a ramp pulse after large depolarization. The slope conductance ranged from 22 to 30 pS, compatible with that of L-type Ca2+ channels. 5. It is concluded that L-type Ca2+ channels in guinea-pig detrusor cells are open for much longer after large depolarizations consistent with their being two channel open states, and that Bay K 8644 prolongs the lifetime of both open states. The underlying mechanisms are discussed.
摘要
在从豚鼠膀胱酶解分离的平滑肌细胞中，采用传统的细胞贴附式膜片钳技术记录Ca2+通道电流。在大多数记录中，膜片电极内含有Bay K 8644（2 microM）。2. 在复极化步骤中观察到的Ca2+通道关闭，在进行大的去极化预处理（+80和100 mV）时显著减慢，无论膜片电极内是否含有Bay K 8644。3. 在大的预处理去极化后（在Bay K 8644存在的情况下）获得的单位Ca2+通道电流轨迹总和显示出缓慢失活的尾电流。4. 利用这种缓慢失活特性，在大的去极化后用斜坡脉冲连续测量单位Ca2+通道电流的电流-电压关系。斜率电导范围为22至30 pS，与L型Ca2+通道的相符。5. 得出结论，豚鼠逼尿肌细胞中的L型Ca2+通道在大的去极化后开放时间长得多，这与其存在两种通道开放状态一致，并且Bay K 8644延长了两种开放状态的寿命。对潜在机制进行了讨论。
