Our recent studies have focused on the processes underlying granule assembly, synthesis and insertion of hormones into granules, movement of granules to sites of secretion and signals leading to membrane contact and fusion between granules and plasma membranes leading to exocytosis in chromaffin cells and Islets of Langerhans. Our work this year has included the characterization of protein kinase and its possible role in hormone secretion from chromaffin cells. In chromaffin cells, the phorbol ester, TPA, induces A23187 but not carbachol and high K+ induced catecholamine secretion. Consistently, TPA also enhanced Ca++ induced catecholamine release from digitonin-permeabilized cells. Phosphoinositide metabolism, believed to be intrinsic to protein kinase C systems, has been found to occur when secretion occurs, but in a delayed fashion, suggesting it also be involved with other aspects of cell function. Synexin, thought to be involved with membrane fusion in secreting cells, has been found to bind to the inner aspect of chromaffin cell plasma membrane in a calcium dependent manner, but also to fuse a chromaffin granule membrane system in a calcium-independent manner. Secreting chromaffin cells have also been mapped by imaging low atomic number elements by electron energy loss spectroscopy. Ascorbate and glucocorticoids have been shown to regulate catecholamine biosynthesis in cultured adrenal chromaffin cells. In islets of Langerhans, it has been found that neighboring cells are electrically coupled, and that cooling dissociates glucose induced insulin release from electrical activity across islet plasma membranes. Glucose was found to cause a rhythmic changes in K+ concentration, coincident with busting pattern of electrical activity. An electrical model for glucose-induced changes in membrane ionic permeability in islets has been devised. The membrane defect in the diabetic mouse mutant Ob/ob has been localized to include K+ channels.
