Effects of synthetic cyclic AMP analogs on amylase exocytosis from rat pancreatic acini

Abstract

Diastereomers of adenosine 3',5'-phosphorothioate activate cAMP-dependent protein kinases (cAMP-PK) in vitro. We found that these compounds are highly selective tools to monitor cAMP-dependent PKA activation and its effect on amylase exocytosis from pancreatic acini. In permeabilized rat acinar cells, (Sp)-cAMPS dose-dependently stimulated amylase secretion, while (Rp)-cAMPS inhibited (Sp)-cAMPS-induced amylase release. In intact rat acini, 8-Br-(Rp)-cAMPS reduced the secretory responses to secretin, vasoactive intestinal polypeptide (VIP), 8-Br-cAMP, and 8-Br-(Sp)-cAMPS, but not to cerulein. Another derivative, dibutyryl-(Rp)-cAMPS, induced a small inhibitory effect against 8-Br-(Sp)-cAMPS and VIP, which was overlapped by an unspecific stimulatory effect on amylase exocytosis induced by the degradation product butyrate. Furthermore, (Sp)-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3',5'- monophosphorothioate ((Sp)-5,6-DCl-cBIMPS), a specific cAMP-PK activator, induced a maximal induction of cAMP-PK activity, but its stimulation of amylase secretion was less than that by secretin. (Sp)-5,6-DCl-cBIMPS regulated the phosphorylation of several proteins, which were also affected by secretin. However, secretin had additional effects. Its action was most likely mediated by a dual effect on the cAMP and the calcium pathway. Our results indicate that the cAMP-dependent pathway is involved in amylase exocytosis from rat pancreatic acini.