Haimann C, Bernheim L, Bertrand D, Bader C R
Department of Physiology, Hôpital Cantonal Universitaire, Geneva, Switzerland.
J Gen Physiol. 1990 May;95(5):961-79. doi: 10.1085/jgp.95.5.961.
Whole-cell voltage clamp and single-channel recordings were performed on cultured trigeminal ganglion neurons from quail embryos in order to study a sodium-activated potassium current (KNa). When KNa was activated by a step depolarization in voltage clamp, there was a proportionality between KNa and INa at all voltages between the threshold of INa and ENa. Single-channel recordings indicated that KNa could be activated already by 12 mM intracellular sodium and was almost fully activated at 50 mM sodium. 100 mM lithium, 100 mM choline, or 5 microM calcium did not activate KNa. The relationship between the probability for the channel to be open (Po) vs. the sodium concentration and the relationship of KNa open time-distributions vs. the sodium concentration suggest that two to three sodium ions bind cooperatively before KNa channels open. KNa channels were sensitive to depolarization; at 12 mM sodium, a 42-mV depolarization caused an e-fold increase in Po. Under physiological conditions, the conductance of the KNa channel was 50 pS. This conductance increased to 174 pS when the intra- and extracellular potassium concentrations were 75 and 150 mM, respectively.
为了研究钠激活钾电流（KNa），对鹌鹑胚胎培养的三叉神经节神经元进行了全细胞膜片钳和单通道记录。当在电压钳中通过阶跃去极化激活KNa时，在INa阈值和ENa之间的所有电压下，KNa和INa之间存在比例关系。单通道记录表明，12 mM细胞内钠即可激活KNa，50 mM钠时几乎完全激活。100 mM锂、100 mM胆碱或5 μM钙均不能激活KNa。通道开放概率（Po）与钠浓度之间的关系以及KNa开放时间分布与钠浓度之间的关系表明，在KNa通道开放之前，两到三个钠离子协同结合。KNa通道对去极化敏感；在12 mM钠时，42 mV的去极化使Po增加e倍。在生理条件下，KNa通道的电导为50 pS。当细胞内和细胞外钾浓度分别为75 mM和150 mM时，该电导增加到174 pS。
