AJP - Renal Physiology, Vol 265, Issue 6 773-F783, Copyright © 1993 by American Physiological Society

ARTICLES

Regulation of cell pH by K+/H+ antiport in renal epithelial cells

M. Graber and E. Pastoriza-Munoz
Veterans Affairs Medical Center, Northport 11768.

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.

This article has been cited by other articles:

				A. Attmane-Elakeb, H. Amlal, and M. Bichara Ammonium carriers in medullary thick ascending limb Am J Physiol Renal Physiol, January 1, 2001; 280(1): F1 - F9. [Abstract] [Full Text] [PDF]

				F. Leviel, D. Eladari, A. Blanchard, J.-S. Poumarat, M. Paillard, and R.-A. Podevin Pathways for HCO-3 exit across the basolateral membrane in rat thick limbs Am J Physiol Renal Physiol, June 1, 1999; 276(6): F847 - F856. [Abstract] [Full Text] [PDF]