Tsai T D, Shuck M E, Thompson D P, Bienkowski M J, Lee K S
Upjohn Laboratories, Kalamazoo, Michigan 49007, USA.
Am J Physiol. 1995 May;268(5 Pt 1):C1173-8. doi: 10.1152/ajpcell.1995.268.5.C1173.
The pH sensitivity of a cloned rat kidney K+ channel, ROMK1, was examined after expression in Xenopus oocytes. Membrane currents and intracellular pH (pHi) were concomitantly monitored by the two-microelectrode voltage-clamp technique and a pH-sensitive microelectrode. Oocytes injected with ROMK1 cRNA developed a hyperpolarized resting potential of -98.7 +/- 0.98 mV and a slightly inwardly rectifying Ba(2+)-sensitive K+ current. Lowering external pH from 7.4 to 6.7 using membrane-permeable acetate buffer reduced measured pHi from 7.2 to 6.6 and reduced the ROMK1 current by 80%. The H+ blockade of ROMK1 currents was voltage independent. The relationship between ROMK1 slope conductance and pHi fitted to a titration curve suggested binding of four H+ to a site with a pK of 6.79. Extracellular acidification from pH 7.4 to 6.0 using membrane-impermeable biphthalate buffer had no effect on the ROMK1 current. The pH sensitivity of the ROMK1 channel is similar to that reported for a small-conductance native kidney K+ channel.
在非洲爪蟾卵母细胞中表达后，对克隆的大鼠肾K⁺通道ROMK1的pH敏感性进行了检测。采用双微电极电压钳技术和pH敏感微电极同时监测膜电流和细胞内pH（pHi）。注射了ROMK1 cRNA的卵母细胞产生了-98.7±0.98 mV的超极化静息电位和轻微内向整流的Ba²⁺敏感K⁺电流。使用膜通透的醋酸盐缓冲液将外部pH从7.4降至6.7，可使测得的pHi从7.2降至6.6，并使ROMK1电流降低80%。ROMK1电流的H⁺阻断与电压无关。ROMK1斜率电导与pHi之间的关系符合滴定曲线，表明四个H⁺与一个pK为6.79的位点结合。使用膜不通透的邻苯二甲酸盐缓冲液将细胞外pH从7.4酸化至6.0对ROMK1电流没有影响。ROMK1通道的pH敏感性与报道的小电导天然肾K⁺通道相似。
