An inward‐rectifying K+ current in clonal rat pituitary cells and its modulation by thyrotrophin‐releasing hormone.
An inward‐rectifying K+ current in clonal rat pituitary cells and its modulation by thyrotrophin‐releasing hormone.
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克隆大鼠垂体细胞中的内向整流钾电流及其通过促甲状腺激素释放激素的调节。
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发表时间：
1990
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通讯作者：
J. Schwarz
中科院分区：
文献类型：
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作者：
C. Bauer;Wolfgang Meyerhof;J. Schwarz
1. 用膜片钳技术记录培养的大鼠肿瘤源性垂体前叶细胞（GH3 细胞）中电压依赖性 K+ 电流。描述了由 K+ 承载的内向整流电流。 2. 在等渗 KCl 中，全细胞内向 K+ 电流是由 ‐40 mV 保持电位的超极化脉冲引起的。这些内向 K+ 电流在负电位超过 ‐60 mV 时表现出时间和电压依赖性失活。在较大的超极化下失活更快、更完全。失活恢复也与时间和电压有关。它更快、更完整，具有更多积极的潜力。失活和从失活恢复的时间过程可以通过单指数拟合。 3. 两个结果表明稳定的内向 K+ 电流存在于 ‐40 mV 处。在强超极化脉冲期间内向 K+ 电流完全失活后，‐40 mV 的保持电流降低，并且在 5 s 的去极化预脉冲后，超极化引起的最大内向 K+ 电流的幅度增加。静息电导估计为最大内向整流电导的 20-30%。 4. Cs+和Ba2+显着降低了内向K+电流，但Ni2+和Co2+则没有显着降低内向K+电流。奎尼丁、4-氨基吡啶和四乙基氯化铵阻断电流。相比之下，树毒素则没有效果。 5. 促甲状腺激素释放激素（TRH）诱导 GH3 细胞中催乳素的双相分泌，在内部 Ca2+ 存在的情况下持续降低内向 K+ 电流。如果移液器溶液含有鸟苷 5'-O-(2-硫代二磷酸) (GDP beta S; 400 microM)，则这种减少作用被消除，从而证实了 G 蛋白参与信号转导途径。 6. TRH 将内向 K+ 电流失活的电压依赖性转移到较小的负电位，导致这些细胞的静息电位范围（‐40 至 ‐60 mV）内出现明显的 K+ 电流失活。 7. 在完整的细胞中，K+通道的关闭会导致去极化。 GH3 细胞中存在内向整流 K+ 电流（该电流能够被 TRH 减少），这可以很容易地解释 TRH 诱导的动作电位放电增加，从而导致持续的第二阶段分泌。
1. Voltage‐dependent K+ currents were recorded in cultured tumour‐derived anterior pituitary cells of the rat (GH3 cells) with the patch clamp technique. An inward‐rectifying current is described which is found to be carried by K+. 2. In isotonic KCl, whole‐cell inward K+ currents were elicited by hyperpolarizing pulses from a holding potential of ‐40 mV. These inward K+ currents showed time‐ and voltage‐dependent inactivation at potentials more negative than ‐60 mV. Inactivation was faster and more complete at larger hyperpolarizations. Recovery from inactivation was also time‐ and voltage‐dependent. It was faster and more complete with more positive potentials. Time course of inactivation and of recovery from inactivation could be fitted by single exponentials. 3. Two results showed that a steady inward K+ current is present at ‐40 mV. The holding current at ‐40 mV was reduced following complete inactivation of the inward K+ current during strong hyperpolarizing pulses, and the amplitude of maximum inward K+ current elicited by hyperpolarization increased after depolarizing pre‐pulses of 5 s. The resting conductance was estimated to be 20‐30% of the maximum inward‐rectifying conductance. 4. The inward K+ current was drastically reduced by Cs+ and Ba2+, but not by Ni2+ and Co2+. Quinidine, 4‐aminopyridine and tetraethylammonium chloride blocked the current. In contrast, dendrotoxin was without effect. 5. Thyrotrophin‐releasing hormone (TRH) which induces biphasic secretion of prolactin in GH3 cells consistently reduced the inward K+ current in the presence of internal Ca2+. This reduction was abolished if the pipette solution contained guanosine 5'‐O‐(2‐thiodiphosphate) (GDP beta S; 400 microM), confirming the involvement of G‐proteins in the signal transduction pathway. 6. TRH shifted the voltage‐dependence of inward K+ current inactivation to less negative potentials resulting in pronounced K+ current inactivation in the range of the resting potential of these cells (‐40 to ‐60 mV). 7. In intact cells, closing of K+ channels would result in a depolarization. The existence of an inward‐rectifying K+ current in GH3 cells which is able to be reduced by TRH could readily explain the TRH‐induced increase in action potential firing underlying the sustained second phase of secretion.