AJP - Cell Physiology, Vol 259, Issue 3 C471-C483, Copyright © 1990 by American Physiological Society
pH regulation and response to AVP in A10 cells differ markedly in the presence vs. absence of CO2-HCO3-
D. Kikeri, M. L. Zeidel, B. J. Ballermann, B. M. Brenner and S. C. Hebert
Harvard Center for the Study of Kidney Diseases, Harvard Medical School, Boston, Massachusetts.
The fluorescent pH-sensitive dye
2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to
determine the effect of ambient CO2-HCO3- on the regulation of
intracellular pH (pHi) and the pHi response to arginine vasopressin (AVP)
in A10 vascular smooth muscle (VSM) cells. Steady-state pHi averaged 7.04
+/- 0.02 in the absence and 7.25 +/- 0.01 in the presence of CO2-HCO3-. In
the absence of CO2-HCO3-, virtually all (greater than 96%) of the acid
extrusion from acidification occurred by amiloride-sensitive Na(+)-H+
exchange. However, in the presence of CO2-HCO3-, acid extrusion after
acidification occurred by both Na(+)-H+ exchange and
4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive
Na(+)-dependent Cl(-)-HCO3- exchange. In CO2-HCO3(-)-containing media,
amiloride-sensitive Na(+)-H+ exchange mediated 85% of acid extrusion at a
pHi of 6.48, but the DIDS-sensitive acid extrusion mechanism
(NA(+)-dependent Cl(-)-HCO3- exchange) was the dominant acid extrusion
mechanism at a pHi of 6.94. Base exited A10 cells by a DIDS-sensitive
process consistent with Na(+)-independent Cl(-)-HCO3- exchange. Both
amiloride- and DIDS-sensitive processes regulated steady-state pHi in
CO2-HCO3-. AVP (10(-7) M) alkalinized steady-state pHi in the absence of
CO2-HCO3- (delta pHi = 0.08 +/- 0.01 pH units) by stimulating Na(+)-H+
exchange; however, AVP did not alter pHi of untreated cells in CO2-HCO3-
(delta pHi = -0.01 +/- 0.01 pH units) because of concomitant stimulation of
Na(+)-independent Cl(-)-HCO3-exchange. We conclude that the steady-state
pHi, the mechanisms of pHi regulation, and the pHi response to AVP in A10
cells are critically influenced by the presence of extracellular CO2-HCO3-.
Thus the potential contribution of pHi changes to VSM cell responses to
vasoactive agents should be evaluated in the presence of CO2-HCO3-.
