The two phases of regulated exocytosis in permeabilized pancreatic acini are modulated differently by heterotrimeric G-proteins.
In this study we examined the influence on AlF4- and GTP gamma S on amylase secretion from alpha toxin permeabilized pancreatic acini. AlF4- only activates heterotrimeric G-proteins, whereas GTP gamma S activates both small ras-like GTP-binding proteins and heterotrimeric G-proteins (Kahn, R. A., J. Biol. Chem., 266, 15595-15597, 1991). GTP gamma S, but not AlF4-, significantly stimulated Ca2(+)-independent amylase secretion, suggesting that a small GTP-binding protein controls regulated exocytosis distal to the site of action of Ca2+. In contrast, both AlF4- and GTP gamma S modulated Ca(2+)-dependent amylase secretion. AlF4- and GTP gamma S stimulated the initial rapid, ATP-independent, phase of Ca(2+)-dependent secretion but inhibited the second slower sustained, ATP-dependent, phase of release. There were significant differences in the GTP gamma S requirements for the stimulation and inhibition of Ca(2+)-dependent amylase secretion, consistent with GTP gamma S activating separate heterotrimeric G-proteins to modulate each phase of the Ca(2+)-dependent secretory response. Our studies also indicated that neither G-protein is a member of the Gi/o class of heterotrimeric G-proteins.
Padfield
P J
PJ
Department of Pathology, St. Louis University Health Sciences Center, Missouri 63104, USA. padfield@wpogate.slu.edu
Panesar
N
N
D000255:Adenosine Triphosphate / Q000494:pharmacology; D017607:Aluminum Compounds / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D005089:Exocytosis / Q000187:drug effects*; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D010179:Pancreas / Q000201:enzymology*; D011487:Protein Conformation; D051381:Rats; D010738:Type C Phospholipases / Q000494:pharmacology; D018631:ras Proteins / Q000502:physiology
D017607:Aluminum Compounds; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000255:Adenosine Triphosphate; D010738:Type C Phospholipases; D000681:Amylases; D019204:GTP-Binding Proteins; D018631:ras Proteins; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride