Calcium and calmodulin stimulate phospholipase A2 and fusion of H,K-ATPase-containing membrane vesicles isolated from pig gastric mucosa.

Fusion of pig gastric H,K-ATPase- and phospholipase A2-containing vesicles in vitro was studied by electron microscopy and by monitoring the change in fluorescence of octadecyl rhodamine B-labelled vesicles. Ca2+ stimulated fusion of the vesicles, and the fusion rate showed a positive correlation with the activity of the phospholipase A2. Both the Ca2(+)-stimulated fusion rate and the Ca2(+)-dependent phospholipase A2 activity were further enhanced by the presence of calmodulin. The present results supported our previous findings (Olaisson et al. 1990) and further indicate that the phospholipase A2 associated with the H,K-ATPase-containing membranes might play a central role in membrane fusion processes in the stimulated parietal cell.