Regulation of cell pH by K+/H+ antiport in renal epithelial cells.
Acid-loaded opossum kidney (OK) cells secrete H+ by Na+/H+ exchange and by a Na(+)- and HCO3(-)-independent pathway that has not been fully characterized. We studied the Na(+)-independent component by measuring H+ flux using the pH-sensitive trapped indicator 2',7'-bis(2-carboxyethyl)-5(6)- carboxyfluorescein. Two Na(+)-independent H(+)-transport systems were identified in acid-loaded cells perfused with HCO3(-)-free buffers. The minor component appears to be a conductive pathway for H+, over 90% inhibitable by 5 mM barium. The major component is stimulated by extracellular K+ and was fully active in the presence of barium, amiloride, ouabain, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and bumetanide and in the absence of Cl-. Ammonium inhibited the H+ flux by 72% at 50 mM, and the H+ flux could be accelerated two- to threefold by limited proteolysis of intact cells using kallikrein or papain. In cells pretreated with barium, the K(+)-induced H+ flux caused no change of bis-oxonol fluorescence, suggesting an electroneutral pathway. The H+ flux was a saturable function of extracellular K+ (Michaelis constant 55 mM), and flux reversed when the K+ gradient was reversed. Similarly, the H+ flux was a linear function of the H+ gradient and reversed when the H+ gradient reversed. Evidence for ongoing K(+)-induced H+ flux was also found in nonacidified cells. First, changing perfusate K+ from 5 to 50 mM alkalinized baseline cell pH, an effect not reproduced by barium despite an equivalent depolarizing effect. Second, increasing perfusate K+ from 5 to 50 mM completely eliminated the acidification produced by 1 mM amiloride. We conclude that the OK cell expresses two Na(+)-independent acid-base transport systems. One is a barium-sensitive electrogenic H+ conductance and the other functions as an electroneutral K+/H+ antiporter. The antiporter is capable of H+ extrusion from acid-loaded cells but in normal cells functions in the reverse direction, as an H+ loader. The K+/H+ antiporter appears to be one of the major systems regulation cell pH in these cells, balancing the H+ efflux mediated by Na+/H+ exchange.
Graber
M
M
Veterans Affairs Medical Center, Northport 11768.
Pastoriza-Munoz
E
E
D000143:Acids / Q000378:metabolism; D000584:Amiloride / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000378:metabolism*; D002460:Cell Line; D002712:Chlorides / Q000494:pharmacology; D004594:Electrophysiology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009893:Opossums; D011188:Potassium / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D027961:Potassium-Hydrogen Antiporters; D012964:Sodium / Q000494:pharmacology
D000143:Acids; D017920:Antiporters; D002712:Chlorides; D027961:Potassium-Hydrogen Antiporters; D011189:Potassium Chloride; D000584:Amiloride; D012964:Sodium; D011188:Potassium