ABSTRACT
Response of inositol phospholipids to the activation of cell surface receptors was first recognized by Hokin and Hokin1 who showed that acetylcholine induces rapid breakdown and resynthesis of phosphatidylinositol in some secretory tissues such as pancreas. The importance of protein phosphorylation in this signal pathway was first demonstrated for serotonin release reaction from platelets, and subsequently for physiological cellular responses in a wide variety of tissues. This chapter summarizes possible roles of protein kinase C in secretory responses. Several other aspects of this protein kinase C have been reviewed. Protein kinase C is distributed in many tissues and organs, with platelets and brain having the highest activity. Protein kinase C preparations obtained from various tissues are apparently similar to one another in their kinetic and catalytic properties. Both phosphatidylcholine and sphingomyelin, on the other hand, decrease the affinity of protein kinase C for Ca2+.
