Effects of a choline-deficient ethionine-supplemented diet on phospholipase C activity in mouse pancreatic acinar cell membranes and in electropermeabilized mouse pancreatic acini.
The nonhydrolyzable guanyl nucleotide GTP gamma S stimulated phosphoinositidase C activity in two preparations obtained from mouse pancreatic acini labeled with myo[2-3H]inositol: a cell-free membrane fraction and intact electropermeabilized acini. This action was dose-dependent, was shared by other nonhydrolyzable guanyl nucleotides such as GMP-phencyclidine hydrochloride and GMP-PMP, as well as by fluoride, and was calcium-independent. Contrarily, no effect was observed even at doses of GTP gamma S as high as 10 microM when the same protocol was repeated on identical acinar preparations from mice fed a choline-deficient, ethionine-supplemented diet. This regimen is known to uncouple secretagogue-receptor occupancy from inositol 1,4,5-trisphosphate generation in pancreatic acinar cells and lead to necrotizing hemorrhagic pancreatitis. These data lead us to conclude that the ethionine-induced inactivation of guanyl nucleotide-dependent pancreatic phosphoinositidase C in pancreatic acinar cells is not the result of either a decrease in GTP level or a decrease in GTP availability. These findings further confirm previous work from this laboratory, which has shown that the biochemical lesion induced by this diet occurs after the agonist-receptor binding step. The diet-induced lesion could be either at the level of the G-protein that couples the enzyme with the receptor or at the level of the phospholipase itself.
Leli
U
U
Department of Surgery, Beth Israel Hospital, Boston, Massachusetts.
Saluja
A
A
Picard
L
L
Zavertnik
A
A
Steer
M L
ML
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002794:Choline / Q000008:administration & dosage*; D004032:Diet; D004558:Electric Stimulation; D005001:Ethionine / Q000494:pharmacology*; D005260:Female; D051379:Mice; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology*; D010738:Type C Phospholipases / Q000378:metabolism*
D010738:Type C Phospholipases; D002794:Choline; D005001:Ethionine