title: Proton-stimulated Cl-HCO3 antiport by basolateral membrane vesicles of lobster hepatopancreas.
abstract: 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.
mesh_terms: D000818:Animals; D000838:Anions / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters; D007700:Kinetics; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008564:Membrane Potentials; D008121:Nephropidae; D009994:Osmolar Concentration; D009995:Osmosis; D010179:Pancreas / Q000378:metabolism* / Q000648:ultrastructure; D011522:Protons; D013268:Stimulation, Chemical
chemical_list: D000838:Anions; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D011522:Protons