Sphingomyelin-metabolizing enzymes and protein kinase C activity in liver plasma membranes of rats fed with cholesterol-supplemented diet.

The effect of cholesterol-supplemented diet on the activities of rat liver plasma membrane sphingomyelin-metabolizing enzymes and protein kinase C was studied. Protein kinase C, phosphatidylcholine:ceramide-phosphocholine transferase, and phosphatidylethanolamine:ceramide-phosphoethanolamine transferase activities were found to increase continuously and almost in parallel during the experimental period on cholesterol diet (days 10, 20, and 30). Linear regression analysis showed a positive correlation between these activities with correlation coefficients r = 0.959 for protein kinase C and phosphatidylcholine:ceramide-phosphocholine transferase, and r = 0.998 for protein kinase C and phosphatidylethanolamine:ceramide-phosphoethanolamine transferase. On the other hand, protein kinase C activation does not correspond to sphingomyelinase activity changes. These data suggest that protein kinase C activation observed in cholesterol-enriched plasma membranes is due to increased production of diacylglycerol and increased acylation of sphingosine to ceramide.