Endothelin-1 (ET-1)-potentiated insulin secretion: Involvement of protein kinase C and the ETA receptor subtype

Endothelin-l (ET-1), a potent vasoconstrictor peptide of endothelial origin , is capable of influencing hormone secretion from endocrine tissues, eg, p ancreatic islet cells. We have shown a direct stimulatory effect of ET-1 on insulin secretion from isolated mouse islets of Langerhans. However, it is unknown as to whether the peptide acts through specific receptors on the i slet cells and which mechanisms are involved in this insulinotropic action. We have therefore used the specific ETA receptor antagonist BQ123, the ETB receptor agonist BQ3020, and classic alpha- and beta-adrenergic and cholin ergic antagonists. ET-1 (100 nmol/L) stimulated insulin secretion from isle ts incubated at 8.3, 11.1, 16.7, and 25 mmol/L glucose (P < .05), At 3.3 mm ol/L glucose, no alteration in insulin secretion was found. The cholinergic receptor antagonist atropine (5 mu mol/L) or the adrenergic receptor antag onists propranolol (5 mu mol/L) or phentolamine (5 mu mol/L) did not affect ET-1 (100 nmol/l)-stimulated insulin secretion. BQ123 (10 pmol/L to 10 mu mol/L) and BQ3020 (1 nmol/L to 1 mu mol/L) had no effect on glucose (16.7 m mol/L)-stimulated insulin secretion, but BQ123 counteracted the stimulatory effect of ET-1 (100 nmol/L) at concentrations of 1 nmol/L to 10 mu mol/L ( P < .01). We also studied the relative role of protein kinase C (PKC) and a Wortmannin-sensitive pathway for ET-l-induced insulin secretion using 12-O -tetradecanoyl phorbol-13-acetate (TPA), Calphostin C, and Wortmannin, resp ectively. At 5.6 mmol/L glucose, ET-l (100 nmol/L) had no effect per se, wh ereas in the presence of 1 mu mol/L TPA, which acutely stimulates PKC, the peptide did potentiate insulin secretion (P < .05). Furthermore, the insuli notropic effect of ET-1 at 16.7 mmol/L glucose was counteracted by the PKC inhibitor Calphostin C (P < .05) and by downregulation of PKC by 24 hours o f exposure of islets to TPA (0.5 mu mol/L, P < .05). Wortmannin (1 mu mol/L ) did not alter ET-1-potentiated insulin secretion. In conclusion, our resu lts suggest that ET-1 acts through specific ET-1 receptors, most likely the ETA, subtype. Furthermore, PKC plays an essential role in the insulinotrop ic action of ET-1 in mouse islets. Copyright (C) 2000 by W.B. Saunders Comp any.