PANCREATIC ACINI POSSESS ENDOTHELIN RECEPTORS WHOSE INTERNALIZATION IS REGULATED BY PLC-ACTIVATING AGENTS

Endothelin-1 (ET-1) and ET-3 mRNA have been found in the pancreas. We investigated the ability of ET-1, ET-2, and ET-3 to interact with and alter dispersed rat pancreatic acinar cell function. Radiolabeled ETs bound in a time- and temperature-dependent fashion, which was specific and saturable. Analysis demonstrated two classes of receptors, one class (ET(A) receptor) had a high affinity for ET-1 but a low affinity for ET-3, and the other class (ET(B) receptor) had equally high affinities for ET-1 and ET-3. No specific receptor for ET-2 was identified. Pancreatic secretagogues that activate phospholipase C (PLC) inhibited binding of I-125-labeled ET-1 (I-125-ET-1) or I-125-ET-3, whereas agents that act through adenosine 3',5'-cyclic monophosphate (cAMP) did not. A23187 had no effect on I-125-ET-1 or I-125-ET-3 binding, whereas the phorbol ester 12-O-tetradecanoylphorbol 13-acetate reduced binding. The effect of cholecystokinin octapeptide (CCK-8) was mediated through its own receptor. Stripping of surface bound ligand studies demonstrated that both I-125-labeled ET-1 and I-125-labeled ET-3 were rapidly internalized. CCK-8 decreased the internalization but did not change the amount of surface bound ligand. Endothelins neither stimulate nor alter changes in enzyme secretion, intracellular calcium, cAMP, or [H-3]inositol trisphosphate (IP3). This study demonstrates the presence of ET(A) and ET(B) receptors on rat pancreatic acini; occupation of both receptors resulted in rapid internalization, which is regulated by PLC-activating secretagogues. Occupation of either ET receptor did not alter intracellular calcium, cAMP, IP3, or stimulate amylase release.