Cellular and subcellular expression of Golf/Gs and Gq/G11 α-subunits in rat pancreatic endocrine cells

Abstract

We studied the cellular and subcellular localization of Gα-subunits in pancreas by immunocytochemistry. Golfα and G11α were specifically localized in islet insulin B-cells and glucagon A-cells, respectively. Gsα and Gqα labeling was more abundant in B-cells. The presence of Golfα in B-cells was confirmed by in situ hybridization. In B-cells, Golfα and Gsα were found in the Golgi apparatus, plasma membrane (PM) and, remarkably, in mature and immature insulin secretory granules, mainly at the periphery of the insulin grains. Gqα was detected on the rough endoplasmic reticulum (RER) near the Golgi apparatus. In A-cells, the Gα-subunits were mostly within the glucagon granules: G11α gave the strongest signal, Gsα less strong, Gq was scarce, and Golf was practically absent. Gqα and Gsα immunoreactivity was detected in acinar cells, although it was much weaker than that in islet cells. The cell-dependent distribution of the Gα-subunits indicates that the stimulatory pathways for pancreatic function differ in acinar and in islet B- and A-cells. Furthermore, the G-protein subunits in islet cell secretory granules might be functional and participate in granule trafficking and hormone secretion.