Sodium bicarbonate cotransport in guinea pig ileal crypt cells.
Macleod, R. John, F. Redican, P. Lembessis, J. R. Hamilton, and M.
Field.
Department of Pediatrics, McGill University-Montreal Children's
Hospital Research Institute, Montreal, Canada H3Z 2Z3 and Departments
of Medicine and of Physiology and Cellular Biophysics, College of
Physicians and Surgeons, Columbia University, New York, NY 10032
APStracts 2:0344C, 1995.
Prior studies show that Ileal HCO3- secretion is of crypt origin,
possibly involving Na-HCO3 cotransport. To test for the latter, we
isolated crypt cells from guinea pig ileum and determined effects of
medium HCO3-, Na+, K+, disulfonic stilbenes and gramicidin on pHi
(BCECF fluorescence), cell volume (electronic sizing) and Na+ efflux
from 22Na+ preloaded cells. Ileal crypt cells alkalinized when placed
in Na-gluconate/HCO3 medium containing methylisobutylamiloride
(1[mu]M), bumetanide (10[mu]M) and DIDS (250[mu]M, which blocks
Cl/HCO3 exchange but not Na-dependent HCO3- uptake). Depolarization
with either gramicidin (50_M) or 50 mM K+ caused a further, SITS
-inhibitable, increase in pHi. Gramicidin also caused SITS-inhibitable
cell swelling. Both gramicidin effects were Na-dependent: At 0 mM
Na+, gramicidin acidified and did not alter cell volume; at 25 mM,
gramicidin also acidified; at 90 and 140 mM, gramicidin alkalinized
and induced cell swelling. A HCO3-dependent, SITS-inhibitable Na+
efflux from 22Na+ preloaded cells was also seen. We conclude that
ileal crypt cells engage in electrogenic Na-HCO3 symport.
Received 8 May 1995; accepted in final form 6 September 1995.
APS Manuscript Number C260-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95