Na:H exchange and the primary H pump in the proximal tubule.
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.
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011190:Potassium Cyanide / Q000494:pharmacology; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*
D001639:Bicarbonates; D002245:Carbon Dioxide; D010042:Ouabain; D012964:Sodium; D011190:Potassium Cyanide