Bichara M, Paillard M, Leviel F, Prigent A, Gardin J P
Am J Physiol. 1983 Feb;244(2):F165-71. doi: 10.1152/ajprenal.1983.244.2.F165.
Cell pH (pHi) transients were monitored at 5-min intervals with the weak acid 5,5-[14C]dimethyloxazolidine-2,4-dione and membrane potentials were estimated from the distribution of [3H]triphenylmethylphosphonium ion in separated proximal tubules (SPT) or rabbit kidney. SPT suspensions were gassed at 37 degrees C first with 5% CO2 and then with 15% CO2. Under normal conditions, pHi rapidly fell during initial 15% CO2 acid loading and then recovered within 20 min. In the presence of 10(-3) M ouabain, which eliminated Na:H exchange as a driving force for H+ secretion, initial cell acidification was still followed by cell pH recovery, which demonstrated a sodium gradient-independent H+ extruding mechanism. In the presence of 10(-3) M ouabain plus 10(-4) M potassium cyanide, there was no pHi recovery following initial cell acidification but, on the contrary, further progressive cell acidification occurred, which is compatible with passive diffusion only of HCO-3 out of the cell. From the cyanide experiments, an apparent permeability coefficient for HCO-3 of the basolateral cell membrane was calculated; this latter result allowed the calculation of rates of passive HCO-3 diffusion and of active H+ extrusion under normal conditions and in the presence of 10(-3) M ouabain. We conclude that in the proximal tubule 1) there is a primary H+ pump additional to Na:H exchange; and 2) this primary H+ pump is responsible for about 25% of active H+ extrusion following acute CO2 cellular acid loading.
用弱酸5,5-[¹⁴C]二甲基恶唑烷-2,4-二酮每隔5分钟监测细胞内pH（pHi）瞬变情况，并根据[³H]三苯基甲基鏻离子在分离的近端小管（SPT）或兔肾中的分布估算膜电位。将SPT悬浮液在37℃下先通入5%二氧化碳，然后通入15%二氧化碳。在正常情况下，在最初的15%二氧化碳酸负荷期间pHi迅速下降，然后在20分钟内恢复。在存在10⁻³M哇巴因的情况下，它消除了钠氢交换作为氢离子分泌的驱动力，最初的细胞酸化之后仍有细胞pH恢复，这表明存在一种不依赖钠梯度的氢离子排出机制。在存在10⁻³M哇巴因加10⁻⁴M氰化钾的情况下，最初的细胞酸化后没有pHi恢复，相反，出现了进一步的渐进性细胞酸化，这仅与碳酸氢根离子从细胞中被动扩散相符。根据氰化物实验，计算出基底外侧细胞膜对碳酸氢根离子的表观渗透系数；后一结果使得能够计算正常情况下以及存在10⁻³M哇巴因时碳酸氢根离子的被动扩散速率和氢离子的主动排出速率。我们得出结论，在近端小管中：1）除了钠氢交换外，还存在一种主要的氢离子泵；2）这种主要的氢离子泵在急性二氧化碳细胞酸化负荷后约占氢离子主动排出的25%。
