Atrial Natriuretic Peptide Affects Stimulus-Secretion Coupling of Pancreatic β-cells

摘要

Atrial natriuretic peptide (ANP) influences glucose ho-meostasis and possibly acts as a link between the cardiovascular system and metabolism, especially in metabolic disorders like diabetes. The current study evaluated effects of ANP on β-cell function by the use of a β-cell-specific knockout of the ANP receptor with guanylate cyclase activity (βGC-A-KO). ANP augmented insulin secretion at the threshold glucose concentration of 6 mmol/L and decreased K_(ATP) single-channel activity in β-cells of control mice but not of βGC-A-KO mice. In wild-type β-cells but not β-cells lacking functional K_(ATP) channels (SUR1-KO), ANP increased electrical activity, suggesting no involvement of other ion channels. At 6 mmol/L glucose, ANP readily elicited Ca~(2+) influx in control β-cells. This effect was blunted in β-cells of βGC-A-KO mice, and the maximal cytosolic Ca~(2+) concentration was lower. Experiments with inhibitors of protein kinase G (PKG), protein kinase A (PKA), phosphodies-terase 3B (PDE3B), and a membrane-permeable cyclic guanosine monophosphate (cGMP) analog on K_(ATP) channel activity and insulin secretion point to participation of the cGMP/PKG and cAMP/PKA/Epac (exchange protein directly activated by cAMP) directly activated by cAMP Epac pathways in the effects of ANP on β-cell function; the latter seems to prevail. Moreover, ANP potentiated the effect of glucagon-like peptide 1 (GLP-1) on glucose-induced insulin secretion, which could be caused by a cGMP-mediated inhibition of PDE3B, which in turn reduces cAMP degradation.