Phospholipase activities of surfactant fractions and their role in the morphological change in surfactants in vitro.

Rat lung surfactants including lamellar body, common myelin and tubular myelin were evaluated for enzyme activities of phospholipase A and phospholipase C using [14C] phosphatidylcholine as the substrate. The metabolic profiles of phosphatidylcholine were correlated with ultrastructural changes of each fraction in vitro incubation to elucidate whether any of these enzymes has a role in the morphological change. Lamellar body showed phospholipase A and phospholipase C activities at neutral pH. Electron microscopic observation showed that although these enzymes had no direct role in change of integration of the lamellar body to lattice tubule, phospholipase C had a role in modulation of the lamellar body to loose lamellae, and phospholipase A had a role in degradation of lattice integration.