Wu S N, Li H F, Chiang H T
Department of Medical Education and Research, Kaohsiung Veterans General Hospital, 386 Ta-Chung 1st Road, 813, Kaohsiung City, Taiwan.
Biochem Pharmacol. 2001 Apr 1;61(7):877-92. doi: 10.1016/s0006-2952(01)00553-6.
The effects of vinpocetine, an inhibitor of cyclic GMP phosphodiesterase, on ionic currents were examined in rat pituitary GH3 lactotrophs with the aid of the patch-clamp technique. In GH3 cells bathed in normal Tyrode's solution, vinpocetine (10 microM) reversibly increased the amplitude of Ca2+-activated K+ current (I(K)Ca) with an EC50 value of 4 microM. When the recording pipettes were filled with 10 mM EGTA, vinpocetine also stimulated I(K)Ca. In the cell-attached configuration, application of vinpocetine to the bath increased the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels. In excised membrane patches, application of vinpocetine (10 microM) to the bath did not change the single-channel conductance of BK(Ca) channels; however, it did increase channel activity. In the inside-out configuration, neither 8-bromo cyclic GMP nor YC-1 applied intracellularly affected BK(Ca) channel activity. The vinpocetine-induced change in the kinetic behavior of BK(Ca) channels was due to an increase in mean open time and a decrease in mean closed time. Vinpocetine (10 microM) caused a leftward shift in the midpoint for the voltage-dependent opening. Under the current-clamp mode, vinpocetine (10 microM) decreased the firing rate of spontaneous action potentials induced by thyrotropin-releasing hormone (10 microM) in GH3 cells. In pheochromocytoma PC12 cells, vinpocetine (10 microM) applied intracellularly also enhanced the activity of BK(Ca) channels without altering single-channel conductance. Thus, the present study suggests that vinpocetine-mediated stimulation of I(K)Ca may result from the direct activation of BK(Ca) channels and indirectly from elevated cytosolic Ca2+.
借助膜片钳技术，在大鼠垂体GH3催乳细胞中研究了环磷酸鸟苷磷酸二酯酶抑制剂长春西汀对离子电流的影响。在浸浴于正常台氏液的GH3细胞中，长春西汀（10 μM）可使钙激活钾电流（I(K)Ca）的幅度可逆性增加，半数有效浓度（EC50）值为4 μM。当记录微电极内充灌10 mM乙二醇双四乙酸（EGTA）时，长春西汀仍可刺激I(K)Ca。在细胞贴附式记录模式下，将长春西汀施加于浴液可增加大电导钙激活钾（BK(Ca)）通道的活性。在膜片切除式记录模式下，将长春西汀（10 μM）施加于浴液不会改变BK(Ca)通道的单通道电导；然而，它确实增加了通道活性。在膜内面向外式记录模式下，细胞内施加8-溴环磷酸鸟苷或YC-1均不影响BK(Ca)通道活性。长春西汀诱导的BK(Ca)通道动力学行为变化是由于平均开放时间增加和平均关闭时间缩短所致。长春西汀（10 μM）使电压依赖性开放的中点向左移位。在电流钳模式下，长春西汀（10 μM）降低了促甲状腺激素释放激素（10 μM）诱导的GH3细胞自发动作电位的发放频率。在嗜铬细胞瘤PC12细胞中，细胞内施加长春西汀（10 μM）也可增强BK(Ca)通道的活性，而不改变单通道电导。因此，本研究提示，长春西汀介导的对I(K)Ca的刺激可能源于BK(Ca)通道的直接激活以及细胞溶质钙升高的间接作用。
