Effects of Phospholipase A and Lysolecithin on Some Electrical Properties of the Muscle Membrane

Albuquerque, E. X. and S. Thesleff. Effects of phospholipase A and lysolecithin on some electrical properties of the muscle membrane. Acta physiol. scand. 1968. 72. 248–252. The effects of incubation with phospholipase A and lysolecithin on the resting membrane potential, action potential, input resistance and acetyleholine sensitivity of isolated extensor digitorum longus and soleus muscles of the rat were compared with those previously obtained with phospholipase C. A common action of the agents studied were that they in sufficient doses depolarized the muscle fibres and reduced the input resistance. In contrast to phospholipase C which irreversibly blocked action potential generation, phospholipase A and lysolecithin had little effect on membrance excitability. The sensitivity of chronically dencrvated muscle fibres to locally applied acetylcholine was unaffected by the two phospholipascs and by Iysolccithin. The difference in action between phospholipasr C and phospholipase A on electrogenic membrane excitability is suggested to be explained by the respective mode of lipolytic action of the two enzymes. Phospholipasc C hydrolyses the diglyceride — phosphate, ester linkage in phosphatides and thereby removes the phosphate head from the molecult while phospliolipase A cleaves one fatty acid ester linking leaving the polar heads of phospholipids intact. Lysolecithin possibly rearranges membrane structures by its high surface activity.