Miyamoto T, Fujiyama R, Okada Y, Sato T
Department of Physiology, Nagasaki University School of Dentistry, Japan.
Brain Res. 1996 Apr 9;715(1-2):79-85. doi: 10.1016/0006-8993(95)01551-5.
Na(+)-dependent K+ conductance observed in apical membrane of isolated bullfrog taste cells was analyzed using various modifications of the patch clamp method. When the apical receptive membrane of a taste cell was exposed to 0.5 M NaCl using a pipette perfusion method, an inward current appeared in the cell-attached patch membrane. The permeability ratio of Na+ to K+ (P(Na)/P(K)) calculated from the reversal potential was 0.3. When an outside-out patch from the receptive membrane was exposed to 0.25 M NaCl solution, two types of K+ channel, whose conductance were 35.8 and 9.4 pS respectively, were activated. These channels were reversibly activated by increasing internal Na+ concentration. In the whole cell configuration, the outward current evoked by a voltage ramp from -80 to 80 mV was significantly suppressed by replacement of Na+ by N-methyl-D-glucamine+ (NMDG+). The Na(+)-dependent outward current was blocked by 10 mM BaCl2, with positive shift of the zero-current potential in the whole cell recordings, indicating that the outward current including Na(+)-dependent K+ component contributes to maintenance of the resting potential. These results suggest that small conductance Na(+)-dependent K+ channels, which are also permeable to Na+, are involved in salt signal transduction in frog taste cells.
使用膜片钳方法的各种改进技术，对分离出的牛蛙味觉细胞顶端膜中观察到的钠依赖钾离子电导进行了分析。当使用移液管灌注法将味觉细胞的顶端感受膜暴露于0.5M NaCl时，在细胞贴附式膜片上出现内向电流。根据反转电位计算得出的钠钾通透率（P(Na)/P(K)）为0.3。当将感受膜的外向膜片暴露于0.25M NaCl溶液时，激活了两种钾离子通道，其电导分别为35.8和9.4 pS。通过增加细胞内钠离子浓度，这些通道被可逆性激活。在全细胞模式下，用N-甲基-D-葡糖胺（NMDG+）替代钠离子，可显著抑制从-80mV到80mV的电压斜坡诱发的外向电流。10mM BaCl2可阻断钠依赖外向电流，全细胞记录中零电流电位出现正向偏移，表明包括钠依赖钾离子成分的外向电流有助于静息电位的维持。这些结果表明，对钠离子也有通透性的小电导钠依赖钾离子通道参与了青蛙味觉细胞中的盐信号转导。
