Amino Acid Uptake and Amylase Secretion in Isolated Rat Pancreatic Lobules In Vitro: Interactions Between Carbachol, Insulin, Phorbor Ester and Ethanol

Abstract

In the present study we examined the effects of bovine insulin, 12-O-teradecanoylphorbol-13-acetate (TPA), carbachol and ethanol on amino acid uptake and amylase secretion from isolated rat pancreatic lobules in vitro. Net L- [³H] serine uptake, assessed relative to D- [¹⁴C] mannitol, was saturable, enhanced by insulin (1 mU/ml) and TPA (10^-6 M) but inhibited by carbachol (10^-5 M) and ouabain (0.1 mM) . Ethanol (65 mM) had no significant effect on L-serine accumulation or amylase release from lobules incubated in the absence or presence of carbachol (10^-5M) . Amylase secretion was markedly stimulated by carbachol, whereas atropine (10^-5 M) simultaneously blocked enzyme secretion and reversed the inhibition of net L-serine uptake induced by carbachol. Basal amylase release was unaffected by insulin but stimulated by TPA. Submaximal concentrations of carbachol (10^-7 M) and TPA (2×10^-8 M) only caused an additive response in amylase secretion. The carbachol-induced depression in net amino acid uptake may reflect enhanced tracer efflux and altered ionic gradients. The similar stimulatory effects provoked by insulin and TPA suggest a possible regulatory role for protein kinase C in enhancing amino acid accumulation in the exocrine pancreas.