ASYMMETRY OF ATTACK BY PHOSPHOLIPASE-C ON THE 2 SIDES OF AN EPITHELIAL MEMBRANE

1. 1. Phospholipase C was applied under standard conditions either to the mucosal or the serosal surfaces of isolated toad bladder epithelium. 2. 2. Following exposure to the enzyme the phospholipids of the bladder epithelium were measured after separation by thin layer chromatography. 3. 3. Phospholipase C caused a significant reduction in the content of phosphatidyleholine compared with controls only when the enzyme was applied to serosal surface. No change in phosphatidylcholine content could be found when the enzyme was applied to the mucosal surface under standard conditions. 4. 4. Treatment of the serosal surface with the enzyme inhibited the increase in hydraulic conductivity across the bladder caused by antidiuretic hormone. 5. 5. It is concluded that either the phospholipid composition of the outer leaflet of the cell membrane is different on the mucosal and serosal surfaces or that the availability of membrane phospholipids to phospholipolytic attack differs on the two sides of the epithelium. If the antagonism of the ADH effect on water flow is due to phospholipolysis then relatively little hydrolysis is required. © 1979.