Evidence for Contribution by Increased Cytoplasmic Na+ to the Insulinotropic Action of PACAP38 in HIT-T15 Cells

• Published in: The Journal of biological chemistry Vol. 273; no. 49; pp. 32602 - 32607
• Main Authors: Filipsson, Karin, Karlsson, Sven, Ahrén, Bo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 04.12.1998; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Cell Line; Cricetinae; Cytoplasm - metabolism; Hydrogen-Ion Concentration; Insulin - metabolism; Neuropeptides - pharmacology; Pituitary Adenylate Cyclase-Activating Polypeptide; Signal Transduction - drug effects; Sodium - metabolism
• DOI: 10.1074/jbc.273.49.32602
• ISSN: 0021-9258

Pituitary adenylate cyclase-activating polypeptide (PACAP) is localized to pancreatic nerve terminals and stimulates insulin secretion. The insulinotropic effect of PACAP38 in insulin-producing HIT-T15 cells is accompanied by increases in cellular cAMP and cytoplasmic Ca2+([Ca2+]cyt). As also intracellular Na+ is important for insulin secretion after glucose and other cAMP forming peptides, we examined the Na+ dependence of the insulinotropic effect of PACAP38 in HIT-T15 cells. We found that PACAP38 (100 nm)-induced insulin secretion was diminished by approximately 50% by removal of extracellular Na+(replaced by equimolar N-methyl-d-glucamine). In contrast, removal of Na+ did not diminish the formation of cellular cAMP (measured by radioimmunoassay) or the increase in [Ca2+]cyt (measured in FURA-2AM-loaded cell suspensions) induced by PACAP38. Furthermore, PACAP-38 increased the cytoplasmic Na+ ([Na+]cyt) in single HIT-T15 cells as measured by the fluorophore sodium-binding benzofran isophthalate. This increase was reduced by removal of extracellular Na+ and by inhibition of protein kinase A by H-89. We conclude that the insulinotropic action of PACAP38 is Na+-dependent. We propose that PACAP38 opens plasma membrane Na+ channels by an action partially mediated by cAMP and protein kinase A, and the subsequent raise in [Na+]cyt elicits insulin secretion by an as yet unsolved mechanism.