Changes in the membrane environment of the (K+ + H+)-ATPase following stimulation of the gastric oxyntic cell.

Biochemical evidence is presented for changes in the membrane environment of the (K+ + H+)-dependent ATPase enzyme of the oxyntic cell following in vivo gastric stimulation of young New Zealand rabbits. The changes are inferred from the marked differences in the sedimentation properties of the (K+ + H+)-ATPase when obtained from homogenates of either stimulated or nonstimulated (resting) fundic gastric epithelium. Stimulation resulted in a redistribution of K+-ATPase activity that was reduced to less than half in the microsomal pellet and concomitantly increased in the membrane fractions normally associated with nuclei and mitochondria. Density gradient fractionation of the mitochondrial pellet yield a preparation rich in (K+ + H+)-ATPase. Our studies indicated that the membranes in this preparation are far larger and apparently denser than the microsomal vesicles associated with the nonstimulated state of the cell. The specific nature of the relationship between stimulation and the observed changes is suggested by the lack of change in the distribution of enzymatic activities unrelated to the apical pole of the oxyntic cell. Preliminary, tentative information aimed at identifying the processes responsible for the observed changes is presented.