Calcium-Regulated Plasma Membrane Rigidification During Corpus Luteum Regression in the Rat

Abstract
Plasma membrane fractions were prepared from ovaries of superovulated rats and examined for structural changes during luteolysis. Using fluorescence polarization, a rapid rigidification in vitro of samples obtained from ovaries undergoing spontaneous or prostaglandin F2 .alpha.-induced regression was observed. The rigidification, manifested by a 72% polarization increase over 50 min, is Ca and calmodulin dependent, temperature sensitive and protein mediated. This increase in polarization did not appear in fractions from nonregressing ovaries; however, addition of phospholipase A2 caused virtually identical changes in polarization results as in samples prepared from regressing ovaries. These results suggest that Ca-calmodulin-dependent phospholipase A2 plays a role in membrane deterioration during luteolysis.