Dissociation of colonic apical na-h exchange activity from bulk
cytoplasmic ph.
Dagher, Pierre C., Thomas Behm, Angela Taglietta-Kohlbrecher, Richard
W. Egnor, and Alan N. Charney.
Nephrology Section, VA Medical Center, New York University School
of Medicine, New York, NY 10010
APStracts 2:0445C, 1995.
Intracellular acidification by stimuli other than CO2 fails to
stimulate colonic apical Na-H exchange and Na absorption. We examined
whether Na absorption could be stimulated in the absence of changes
in cytoplasmic pH (pHi). Distal colon of male Sprague-Dawley rats was
used for pHi measurements with BCECF and for flux measurements in
Ussing chambers. In 21 mM HCO3-Ringers, increasing PCO2 from 20 to 70
mmHg decreased pHi from 7.51 to 7.03 and increased net Na flux (Jt)
from 4.2 +/- 0.4 to 6.8 +/- 0.6 [mu]eq/cm2.h. Similar increases in Jt
occurred in the absence of mucosal Cl and in the presence of
phalloidin to inhibit microfilaments, or benzolamide to inhibit
membrane-bound carbonic anhydrase. Isohydric increases in PCO2 did
not alter pHi but stimulated Jt from 5.1 +/- 0.6 to 7.2 +/- 0.8
[mu]eq/cm2.h. CCCP decreased pHi from 7.45 to 7.35 but did not
stimulate Jt. Butyrate (25 mM) decreased pHi from 7.15 to 7.02 with
recovery to baseline within 6 min; however, Jt increased by 2.2
[mu]eq/cm2.h for 60 min. We conclude that apical Na-H exchange
activity is unresponsive to changes in bulk cytoplasmic pH, and is
independent of Cl-HCO3 exchange, microfilaments and membrane-bound
carbonic anhydrase. The presence of a hydrogen-tight, CO2 and
butyrate-permeable subapical domain is postulated.
Received 25 October 1995; accepted in final form 5 December 1995.
APS Manuscript Number C649-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95