Amylase release from streptolysin O permeabilized fetal pancreatic acini

Abstract

Developmental regulation of Ca(2+)-dependent protein discharge was investigated in fetal and neonatal rat pancreatic acini permeabilized with streptolysin O. When incubated at 37 degrees C in a Ca(2+)-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid/K glutamate buffer, permeabilized day 19 and 20 fetal acini demonstrated Ca(2+)-dependent release of amylase, whereas day 21 (term) fetal acini did not. Ca(2+)-dependent amylase release reappeared in day 1, 2, and 6 neonatal pancreases. ATP depletion completely inhibited Ca(2+)-stimulated amylase release from both day 20 fetal and adult acini. Ca(2+)-dependent amylase discharge from day 20 fetal acini was enhanced by the nonhydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), and by the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA). Ca(2+)-independent GTP gamma S-stimulated amylase release was observed from adult but not from day 20 fetal acini. In contrast to its stimulatory effects in permeabilized adult acini, adenosine 3',5'-cyclic monophosphate (cAMP) alone had little effect on release from permeabilized day 20 fetal acini. Our studies indicate that the fetal pancreas is competent to undergo Ca(2+)-dependent protein secretion but that this secretion is suppressed at birth. Our studies also suggest that the fetal gland is sensitive to modulators of exocytosis active in the adult pancreas, such as GTP gamma S, TPA, and cAMP but responds differently to these agents compared with responses in adult glands.