Lmmunohistochemical localization of monoamine oxiclase type B in pancreatic islets of the rat

摘要

Monoamine oxidase (MAO) is regarded as a mitochondrial enzyme. This zyme localizes on the outer membrane of mitochondria. There are two kinds of isozymes, MAO type A (MAOA) and type B (MAOB). Previous studies have shown MAOB activity is found in the pancreatic islets. This activity in the islets is increased by fasting-induced decrease of plasma glucose level. Islet B cells contain monoamines in secretory granules. These monoamines inhibit the secretion of insulin from the B MAOB is active in degrading monoamines. Therefore, MAOB may influence the secretory process by regulating the stores of monoamines in the B cells. However, it has been determined whether MAOB is localized on B cells or other cell types of the islets. the present study, we used both double-labeling immunofluorescence histochemical electron microscopic immunohistochemical methods to examine the subcellulartion of MAOB in rat pancreatic islets. MAOB was found in the mitochondrial membranes of glucagon-secreting cells (A cells), insulin-secreting cells (B cells), and pancreatic polypeptide (PP)-secreting cells (PP cells), but no MAOB was found in statin-secreting cells (D cells), nor in certain other PP cells. There were two kinds of chondria in pancreatic islet B cells: one contains MAOB on their outer membranes, but substantial proportion of them lack this enzyme. Our findings indicate that islet B cells contain MAOB on their mitochondrial outer membranes, and this enzyme be involved in the regulation of monoamine levels and insulin secretion in the B cells.