Okabe K, Inoue Y, Kawarabayashi T, Kajiya H, Okamoto F, Soeda H
Department of Oral Physiology, Fukuoka Dental College, Japan.
Pflugers Arch. 1999 Dec;439(1-2):76-85. doi: 10.1007/s004249900140.
The properties of hyperpolarization-activated current in pregnant rat uterus (17-19 days gestation) were investigated using microelectrode and patch-clamp techniques, and isometric tension recording. The resting membrane potentials were -58.4 mV and -48.5 mV in longitudinal and circular muscle cells, respectively. Application of hyperpolarizing current pulses produced a time-dependent anomalous inward rectification of membrane potential only in circular muscle cells. Under voltage-clamp conditions, inward currents (Ih) were activated by long hyperpolarizing pulses below -60 mV in circular but not in longitudinal muscle cells. Application of extracellular but not intracellular Cs+ reduced the amplitude of I(h) in a concentration-dependent manner (an IC50( of 0.15 mM). The reversal potential for Ih was -26.2 mV and the slope conductance was 5 nS/pF. Changes in [K+]o and [Na+]o shifted the reversal potential, and Ih amplitude increased with excess [K+]o and decreased with low [Na+]o. The steady-state activation of Ih was well fitted by a Boltzmann equation with a half-activation potential of -84.3 mV and a slope factor of 9.6 mV. Time courses of activation and deactivation of the current strongly depended on membrane potential, and were well fitted by a single exponential function. The activation time constant of Ih was dependent on temperature. In isometric tension recording, application of extracellular Cs+ to the circular muscles reduced the frequency, but not the amplitude, of spontaneous contractions in a concentration-dependent manner. It is concluded that in pregnant rat uterus Ih channels are predominantly distributed in smooth muscle cells from the circular layer. Since Ih is activated at the resting membrane potential, it is likely that this current contributes to the maintenance of resting membrane potential and spontaneous activity in circular smooth muscle cells of late pregnant rats.
采用微电极、膜片钳技术和等长张力记录法，研究了妊娠大鼠子宫（妊娠17 - 19天）超极化激活电流的特性。纵行肌细胞和环行肌细胞的静息膜电位分别为-58.4 mV和-48.5 mV。施加超极化电流脉冲仅在环行肌细胞中产生膜电位随时间变化的反常内向整流。在电压钳条件下，长时超极化脉冲（低于-60 mV）可激活环行肌细胞而非纵行肌细胞的内向电流（Ih）。细胞外而非细胞内施加Cs + 可浓度依赖性地降低I(h)的幅度（IC50为0.15 mM）。Ih的反转电位为-26.2 mV，斜率电导为5 nS/pF。细胞外[K + ]o和[Na + ]o的变化使反转电位发生偏移，Ih幅度随[K + ]o升高而增加，随[Na + ]o降低而减小。Ih的稳态激活可用玻尔兹曼方程很好地拟合，半激活电位为-84.3 mV，斜率因子为9.6 mV。电流的激活和失活时间进程强烈依赖于膜电位，且可用单指数函数很好地拟合。Ih的激活时间常数依赖于温度。在等长张力记录中，向环行肌施加细胞外Cs + 可浓度依赖性地降低自发收缩的频率，但不影响其幅度。结论是，在妊娠大鼠子宫中，Ih通道主要分布于环行肌层的平滑肌细胞。由于Ih在静息膜电位时被激活，该电流可能有助于维持妊娠晚期大鼠环行平滑肌细胞的静息膜电位和自发活动。
