AJP - Renal Physiology, Vol 258, Issue 4 883-F892, Copyright © 1990 by American Physiological Society
Intracellular pH regulates Na(+)-independent Cl(-)-base exchange in JTC-12 (proximal tubule) cells
I. Fineman, D. Hart and E. P. Nord
Department of Medicine, School of Medicine, State University of New York, Stony Brook 11794.
The role of an anion exchange pathway in the regulation of intracellular pH
(pHi) under alkaline load and steady-state conditions and the modulation of
this transporter by pHi was investigated in confluent monolayers of cloned
JTC-12 cells, derived from monkey kidney proximal tubule. Regulation of pHi
was fluorometrically monitored using the pH-sensitive probe,
2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Monolayers in
which pHi was rapidly elevated by removal of HCO3(-)-CO2 from the bathing
medium demonstrated an absolute requirement for Cl- to recover toward
base-line pHi. The recovery process proceeded in the absence of Na+, was
inhibited 80% by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and was
unaffected by 10(-4) M amiloride. When extracellular pH (pHo) was serially
lowered from 7.4 to 6.7, recovery from an alkaline load induced by removal
of HCO3(-)-CO2 from the medium occurred only when pHi was elevated above
approximately 7.25. Below pHi approximately 7.25 no recovery toward initial
pHi was observed. When pHi was elevated above approximately 7.25 with pHo
maintained at 6.7, the recovery process ceased at pHi approximately 7.25
despite favorably oriented Cl- and OH- chemical gradients. Consistent with
these observations, removal of Cl- from the medium of cells buffered with
25 mM HCO3(-)-5% CO2 at pHo 7.4 (in the absence of Na+) resulted in
reversible elevation of pHi, whereas in a solution buffered to pHo 6.7 with
5 mM HCO3(-)-5% CO2, removal of Cl- failed to elevate pHi. Under
steady-state conditions in the presence of 25 mM HCO3(-)-5% CO2 at pHo 7.4,
pHi was 7.40 +/- 0.02 and reversibly decreased to 7.23 +/- 0.01 on removal
of Na+ (in the presence of amiloride) from the bathing medium, indicating
that the Cl(-)-base exchanger is operative under basal conditions and
functions as a base extruder. In summary the JTC-12 cell possesses a
Na(+)-independent Cl(-)-base exchange mechanism that is operative under
alkaline load and steady-state conditions. pHi but not pHo modulates the
activity of this transport pathway, and below pHi approximately 7.25 the
exchanger is quiescent.
