Immunohistochemical Localization of Monoamine Oxidase Type B in Pancreatic Islets of the Rat
Yu-Hong Huang 1, Akio Ito 1 and Ryohachi Arai 1*
1 Department of Anatomy, Shiga University of Medical Science, Otsu, Shiga, Japan (Y-HH,RA), and Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, Fukuoka, Japan (AI)
* To whom correspondence should be addressed. E-mail: rarai{at}belle.shiga-med.ac.jp.
Submitted on February 20, 2005
Accepted on 13 April 2005
 |
Abstract |
|---|
Monoamine Oxidase (MAO) is regarded as a mitochondrial enzyme. This enzyme localizes on the outer membrane of mitochondria. There are two kinds of MAO isozymes, MAO type A (MAOA) and type B (MAOB). Previous studies have shown that MAOB activity is found in the pancreatic islets. This activity in the islets is increased by the fasting-induced decrease of plasma glucose level. Islet B-cells contain monoamines in their secretory granules. These monoamines inhibit the secretion of insulin from the B-cells. MAOB is active in degrading monoamines. Therefore, MAOB may influence the insulin-secretory process by regulating the stores of monoamines in the B-cells. However, it has not been determined whether MAOB is localized on B-cells or other cell types of the islets. In the present study, we used both double-labeling immunofluorescence histochemical and electron microscopic immunohistochemical methods to examine the subcellular localization of MAOB in rat pancreatic islets. MAOB was found in the mitochondrial outer membranes of glucagon-secreting cells (A-cells), insulin-secreting cells (B-cells), and some pancreatic polypeptide (PP)-secreting cells (PP-cells), but no MAOB was found in somatostatin-secreting cells (D-cells), nor in certain other PP-cells. There were two kinds of mitochondria in pancreatic islet B-cells. One containing MAOB on their outer membranes, but a substantial proportion of them lacking this enzyme. Our findings indicate that pancreatic islet B-cells contain MAOB on their mitochondrial outer membranes, and this enzyme may be involved in the regulation of monoamines levels and insulin secretion in the B-cells.
Key Words:
MAO, glucagons, insulin, somatostatin PP rat, pancreas, mitochondria double-labeling immunofluorescence Histochemistry, electron microscopic immunohistochmistry
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?