RODENT PANCREATIC-ISLET CELLS CONTAIN THE CALCIUM-BINDING PROTEINS CALCINEURIN AND CALRETININ

Calcium is known to be of critical importance for hormone secretion in the insulin-producing B-cells of the endocrine pancreas. Calcium-medi ated intracellular signal transduction and the regulation of the conce ntration of free calcium in B-cells probably involve calcium-binding p roteins. In the present study, we have investigated the expression of the calcium/calmodulin-dependent phosphatase, calcineurin, and the EF- hand calcium-binding protein, calretinin, in pancreata of hamsters, ge rbils, and rats by immunocytochemistry. Immunocytochemical investigati ons of serial semithin sections of plastic-embedded pancreata revealed that calcineurin and calretinin were constantly present in islet cell s of all three species. In addition to B-cells, these proteins could a lso be detected in glucagon (A-), somatostatin (D-), and pancreatic po lypeptide (PP-) cells. Non-B-cells, especially glucagon-producing A-ce lls, often exhibited a significantly higher degree of immunoreactivity for both calcium-binding proteins than B-cells. Thus, calcineurin and calretinin may play distinct roles in the regulation of calcium-depen dent secretory activities of the different pancreatic endocrine cell t ypes.