Munakata M, Fujimoto M, Jin Y H, Akaike N
Department of Pediatrics, Tohoku University School of Medicine, Sendai 980-77, Japan.
Brain Res. 1998 Aug 3;800(2):282-93. doi: 10.1016/s0006-8993(98)00533-2.
The electrogenic Na/K pump current (Ip) was studied in the dissociated neostriatal neurons of the rat by using the nystatin-perforated patch recording mode. The Ip was activated by external K+ in a concentration-dependent manner with an EC50 of 0.7 mM at a holding potential (VH) of -40 mV. Other monovalent cations also caused Ip and the order of potency was Tl+>K+, Rb+>NH4+, Cs+>>>Li+. The Ip decreased with membrane hyperpolarization in an external solution containing 150 mM Na+, while the Ip did not show such voltage dependency without external Na+. Ouabain showed a steady-state inhibition of Ip in a concentration- and temperature-dependent manner at a VH of -40 mV. The IC50 values at 20 and 30 degrees C were 7.1 x 10(-6) and 1.3 x 10(-6) M, respectively. The decay of Ip after adding ouabain well fitted with a single exponential function. At a VH of -40 Mv, the association (k+1) and dissociation (k-1) rate constants estimated from the time constant of the current decay at 20 degrees C were 4.0 x10(2) s-1 M-1 and 6.3 x 10(-3) s-1, respectively. At 30 degrees C, k+1 increased to 2.8 x 10(3) s-1 M-1 while k-1 showed no such change with a value of 1.8 x 10(-3) s-1. A continuous Na+ influx was demonstrated by both the Na+-dependent leakage current and tetrodotoxin-sensitive Na+ current, which resulted in the continuous activation of the Na/K pump. It was thus concluded that the Na/K pump activity was well-maintained in the dissociated rat neostriatal neurons with distinct functional properties and that the activity of the pump was tightly connected with Na+ influxes.
采用制霉菌素穿孔膜片钳记录模式，对大鼠离体新纹状体神经元的生电钠钾泵电流（Ip）进行了研究。Ip由细胞外K+以浓度依赖方式激活，在-40 mV的钳制电位（VH）下，其半数有效浓度（EC50）为0.7 mM。其他单价阳离子也可引起Ip，其效力顺序为：Tl+>K+，Rb+>NH4+，Cs+>>>Li+。在含有150 mM Na+的细胞外溶液中，Ip随膜超极化而降低，而在无细胞外Na+时，Ip不显示这种电压依赖性。哇巴因在-40 mV的VH下，以浓度和温度依赖方式对Ip产生稳态抑制。20℃和30℃时的半数抑制浓度（IC50）值分别为7.1×10^(-6) M和1.3×10^(-)(6) M。加入哇巴因后Ip的衰减很好地拟合为单指数函数。在-40 mV的VH下，根据20℃时电流衰减的时间常数估算的结合（k+1）和解离（k-1）速率常数分别为4.0×10^(2) s^(-1) M^(-1)和6.3×10^(-3) s^(-1)。在30℃时，k+1增加到2.8×10^(3) s^(-1) M^(-1)，而k-1没有变化，值为1.8×10^(-3) s^(-1)。钠依赖性漏电流和河豚毒素敏感性钠电流均证明有持续的Na+内流，这导致钠钾泵的持续激活。因此得出结论，钠钾泵活性在离体大鼠新纹状体神经元中得到良好维持，具有独特的功能特性，且泵的活性与Na+内流紧密相关。
