Effect of carbachol or histamine stimulation on rat gastric membranes enriched in (H +-K +)-ATPase

Abstract

We have examined histamine- or carbachol-induced changes in rat gastric membranes enriched in K +-stimulated ATPase. Stimulation of secretion by both secretagogues in vivo produced a class of microsomal membranes which exhibited valinomycin-independent, KCl-dependent H + transport. In contrast, membrane vesicles isolated from cimetidine inhibited resting mucosa exhibited largely the ionophore-dependent H + transport. In addition, only in the carbachol-stimulated membranes a portion of the ionophore-independent H + transport was refractory to cimetidine pretreatment. The gastric microsomal membranes were resolved into light and heavy fractions by centrifugation over isotonic 2H 2O media. The ionophore-independent H + transport was almost exclusively associated with the heavy microsomal fraction while the ionophore-dependent H + transport was detected in the light fraction. Also, these fractions were considerably different from each other in their appearance in electron micrographs and SDS gel electrophoresis patterns. Secretagogue stimulation increased the population of the heavy microsomal membrane vesicles exhibiting the valinomycin-independent, K +-dependent H + transport and their overall content of K +-stimulated ATPase. Cimetidine treatment, on the other hand, increased the ATPase activity associated with the light microsomes, and produced the heavy microsomal membranes showing only a marginal degree of the ionophore independent H + accumulation, even though they were very similar to the carbachol-stimulated heavy membranes in the specific activity of K +-stimulated ATPase, SDS gel patterns and appearance in electron micrograph. These observations suggest that activation of secretion involves at least two distinctive events; transformation of the light to the heavy gastric membranes containing a K +-dependent H + pump and an increased KCl permeability in the latter.