Zushi I, Shimura M, Tamai M, Kakazu Y, Akaike N
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Neuropharmacology. 1998 Aug;37(8):1053-61. doi: 10.1016/s0028-3908(98)00084-7.
The electrogenic Na+ -K+ pump current (Ip) in carp bipolar cells was investigated under voltage-clamp conditions. The Ip was activated in a concentration-dependent manner by adding external K+ (Ko+) and was completely suppressed with 10(-4) M ouabain (EC50=1.23 mM; Hill coefficient=1.36). The Ip was suppressed in a concentration-dependent manner by ouabain (IC50=1.90 mM; Hill coefficient=0.93). The Ip did not show a distinct voltage dependency either with or without Na(o)+. A large outward shift of the holding current was observed by completely removing Na(o)+. In the presence of Na(o)+, a steady Ip was observed even in the absence of internal Na+ (Na(i)+). These results suggest that continuous Na+ influxes exist across the membrane. When external and internal Na+ was removed, a transient Ip was observed (half decay time (t1/2) was 5.0+/-0.6 s), thus indicating that the transient Ip was activated by the residual Na(i)+. In the absence of Na(o)+, the transient Ip was also observed with lower than 8 mM Na(i)+. The t1/2 depended on Na(i)+. However, a steady Ip was observed with 10 mM Na(i)+ or more. The functional properties of the Ip are discussed.
在电压钳制条件下研究了鲤鱼双极细胞中的生电钠钾泵电流（Ip）。通过添加细胞外钾离子（Ko+），Ip以浓度依赖性方式被激活，并且在10（-4）M哇巴因存在下被完全抑制（半数有效浓度（EC50）=1.23 mM；希尔系数=1.36）。Ip被哇巴因以浓度依赖性方式抑制（半数抑制浓度（IC50）=1.90 mM；希尔系数=0.93）。无论有无细胞外钠离子（Na(o)+），Ip均未表现出明显的电压依赖性。通过完全去除细胞外钠离子观察到钳制电流出现大幅外向偏移。在存在细胞外钠离子的情况下，即使在没有细胞内钠离子（Na(i)+）时也观察到稳定的Ip。这些结果表明跨膜存在持续的钠离子内流。当去除细胞外和细胞内钠离子时，观察到一个瞬时Ip（半衰期（t1/2）为5.0±0.6秒），因此表明瞬时Ip是由残余的细胞内钠离子激活的。在没有细胞外钠离子的情况下，当细胞内钠离子低于8 mM时也观察到瞬时Ip。t1/2取决于细胞内钠离子。然而，当细胞内钠离子为10 mM或更高时观察到稳定的Ip。对Ip的功能特性进行了讨论。
