Nakayama S, Brading A F
University Department of Pharmacology, Oxford, United Kingdom.
Am J Physiol. 1995 Jul;269(1 Pt 1):C48-54. doi: 10.1152/ajpcell.1995.269.1.C48.
The whole cell patch-clamp technique was used to measure Ca2+ current in isolated smooth muscle cells from guinea pig urinary bladder. Noniactivating Ca2+ channel current was modeled incorporating the long open state of the Ca2+ channel. When inactivation was examined over a wide voltage range, a completely U-shaped curve was obtained. Lack of inactivation at +80 mV could be attributed to the long open state induced by large depolarization as well as to minimal Ca2+ influx and Ca(2+)-dependent inactivation. Activation parameters were obtained by comparing the amplitudes of conditioned (by +80 mV, 5 s) and unconditioned test potentials. With the use of the activation curve and the U-shaped inactivation curve, a noninactivating current that peaks around +20 mV was obtained. This current is composed of a so-called "window" current and a persistent current brought about by the long open state. Differences in the voltage dependence of the development of the long open state in various smooth muscles, as well as differences in the equilibrium constant between open and inactivated states, could underlie the different patterns of contractile behavior that characterize smooth muscles.
采用全细胞膜片钳技术测量豚鼠膀胱分离平滑肌细胞中的Ca2+电流。通过纳入Ca2+通道的长开放状态对非失活性Ca2+通道电流进行建模。当在较宽电压范围内检测失活情况时，得到了一条完全呈U形的曲线。在+80 mV时缺乏失活可归因于大去极化诱导的长开放状态以及最小的Ca2+内流和Ca(2+)依赖性失活。通过比较经+80 mV、5 s预处理和未经预处理的测试电位的幅度来获得激活参数。利用激活曲线和U形失活曲线，获得了在+20 mV左右达到峰值的非失活性电流。该电流由所谓的“窗口”电流和长开放状态产生的持续性电流组成。各种平滑肌中长开放状态发展的电压依赖性差异以及开放态与失活态之间平衡常数的差异，可能是平滑肌收缩行为不同模式的基础。
