AJP - Renal Physiology, Vol 262, Issue 5 897-F901, Copyright © 1992 by American Physiological Society
Extracellular pH modifies adaptive response to high K+ in cultured canine kidney cells
M. A. Manuli and J. M. Lorenz
Department of Radiology, University of Rochester Medical Center, New York 14642.
The chronic interactive and independent effects of extracellular pH and K+
on renal Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity and active K+
transport were studied in the Madin-Darby canine kidney (MDCK) cell line.
Confluent cell monolayers were incubated for 24 h in control (4 mM) or high
(7.5 mM) K+ medium at acid (6.8) or neutral (7.4) pH. Under acid pH
conditions, exposure to high K+ elicited a rise of 133% in maximum
Na(+)-K(+)-ATPase activity and 66% in active K+ uptake. In contrast, high
K+ had no effect on enzyme activity or K+ uptake at neutral pH.
Detergent-activated Na(+)-K(+)-ATPase assay demonstrated a latent pool of
enzyme at acid pH-control K+, which seemed to account entirely for the
increase in Na(+)-K(+)-ATPase activity after exposure to high K+. The
effects of pH appeared unrelated to HCO3- and Cl- concentration in the
extracellular environment. We conclude that the upregulatory effect of high
K+ on renal Na(+)-K(+)-ATPase is pH dependent. The data suggest that a pool
of catalytically inactive enzyme exists only at acid extracellular pH at K+
concentrations in the normal physiological range and that K+ adaptation, at
least initially, is the result of recruitment of this latent intracellular
pool. In the intact cell extracellular K+ and luminal pH may interact to
modify catalytic turnover rate as well as bioavailability of
Na(+)-K(+)-ATPase.
