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.

Occurrence of phospholipase A2 and lysophospholipase in a gastric H,K-ATPase-containing membrane fraction, and the formation of lysophosphatidylcholine in stimulated pig parietal cells.

A membrane fraction containing H,K-ATPase (EC 3.6.1.

Phospholipid organization in H,K-ATPase-containing membranes from pig gastric mucosa.

The transverse distribution of the phospholipids in vesicular H+-translocating membranes prepared from pig gastric mucosa was investigated with the aid of phospholipase C, sphingomyelinase, and trinitrobenzenesulfonic acid. The major part (80-90%) of the phosphatidylcholine and the phosphatidylethanolamine, 60% of the phosphatidylserine, and 45% of the sphingomyelin was located on the external, cytoplasmic side of the vesicle membranes. After treatment with phospholipase C the vesicles still behaved as osmometers and appeared as closed vesicles on the electron micrographs.

Distribution of carbonic anhydrase in cells and membranes isolated from pig gastric mucosa.

Mucosal cells were isolated from pig stomachs and then fractionated on linear density gradients of Percoll. Different types of cells were identified by their typical staining and morphology. In disrupted cell fractions, hydration of CO2 by carbonic anhydrase was measured by means of pH-stat technique.

Characterization of proton-transporting membranes from resting pig gastric mucosa.

Membrane vesicles were purified from resting corpus mucosa of pig stomachs by velocity-sedimentation on a sucrose-Ficoll step gradient. Two vesicular fractions containing the (H+ + K+)-ATPase were obtained. One fraction was tight towards KCl, the other was leaky.