title: Finding of a KCl-independent, electrogenic, and ATP-driven H+-pumping activity in rat light gastric membranes and its effect on the membrane K+ transport activity.
abstract: Resting rat light gastric membranes prepared through 2H2O and Percoll gradient centrifugations were enriched not only with (H+-K+)-ATPase and K+ transport activity (Im, W. B., Blakeman, D. P., and Davis, J. P. (1985) J. Biol. Chem. 260, 9452-9460), but also with a K+-independent, ATP-dependent H+-pumping activity. This intravesicular acidification has been ascribed to an oligomycin-insensitive H+-ATPase which differed from (H+-K+)-ATPase in several respects. The H+-ATPase is electrogenic, apparently of lower capacity, required a lower optimal ATP concentration (4 microM for the H+-ATPase and 500 microM for (H+-K+)-ATPase), of lower sensitivity to vanadate and sulfhydryl agents such as p-chloromercuribenzoate and N-ethylmaleimide, and insensitive to SCH 28,080, a known competitive inhibitor of (H+-K+)-ATPase with respect to K+. Operation of the H+-ATPase, however, appeared to interfere with the K+ transport activity in the light gastric membranes, probably through development of intravesicular positive membrane potential; for example, micromolar levels of Mg2+-ATP fully inhibited K+ uptake and stimulated K+ efflux as measured with 86Rb+. Involvement of (H+-K+)-ATPase in the K+ transport is not likely, since the inhibitory effect of Mg2+-ATP continued even after removal of the nucleotide with an ATP-scavenging system. Moreover, nigericin, an electroneutral H+/K+ exchanger, could bypass the inhibitory effect of Mg2+-ATP and equilibrate the membrane vesicles with 86Rb+ while valinomycin, an electrogenic K+ ionophore, could not. Finally, the H+-ATPase could possibly be involved in the acid secretory process, since its H+-pumping activity was removed from the light gastric membrane fraction upon carbachol treatment, along with the K+ transport and (H+-K+)-ATPase activities. We have speculated that the H+-ATPase is responsible for maintaining the K+-permeable intracellular membrane vesicles acidic and K+ free during the resting state of acid secretion and may contribute to basal acid secretion.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D005753:Gastric Mucosa / Q000378:metabolism*; D017506:H(+)-K(+)-Exchanging ATPase; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D051381:Rats; D012413:Rubidium / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D014639:Vanadium; D014634:Valinomycin; D014638:Vanadates; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D006180:Proton-Translocating ATPases; D012413:Rubidium