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Am J Physiol Regul Integr Comp Physiol 252: R859-R870, 1987;
0363-6119/87 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 5 859-R870, Copyright © 1987 by American Physiological Society

ARTICLES

Proton-stimulated Cl-HCO3 antiport by basolateral membrane vesicles of lobster hepatopancreas

G. A. Ahearn, M. L. Grover, R. T. Tsuji and L. P. Clay

Purified epithelial basolateral membrane vesicles were prepared from lobster hepatopancreas by sorbitol gradient centrifugation. Na+-K+-adenosinetriphosphatase, alkaline phosphatase, and cytochrome-c oxidase enzyme activities in the final membrane preparation were enriched 9.6-, 1.4-, and 0.4-fold, respectively, compared with their activities in the original tissue homogenate. Vesicle osmotic reactivity was demonstrated using 60-min equilibrium 36Cl uptake experiments at a variety of transmembrane osmotic gradients. 36Cl uptake into vesicles preloaded with HCO3 was significantly greater than into vesicles lacking HCO3. This exchange process was stimulated by a transmembrane proton gradient (internal pH greater than external pH). Proton-gradient-dependent Cl-HCO3 exchange was potential sensitive and stimulated by an electrically negative vesicle interior. 36Cl influx (4-s exposures) into HCO3-loaded vesicles occurred by the combination of 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid sensitive, carrier-mediated transfer and "apparent diffusion." 36Cl influx was a hyperbolic function of both internal [HCO3] and internal [Cl]. The two internal anions displayed a 100-fold difference in apparent affinity constants with HCO3 being strongly preferred. 36Cl influx was stimulated more by preloaded monovalent than by divalent anions. Na was an inhibitor of proton-dependent anion antiport, whereas K had no effect. A model for HCl-HCO3 antiport is suggested that employs combined transmembrane concentration gradients of Cl and HCO3 to power anion exchange and transfer protons against a concentration gradient.


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