GTP‐induced fusion of isolated pancreatic microsomal vesicles is increased by acidification of the vesicle lumen

Publisher Website
Google Scholar
Abstract
Using the ‘fusogen’ polycthyleneglycol (PEG), Dawson et al. [1] have concluded that both guanosine triphosphate (GTP)-mduced calcium efflux and the enhancement of IP3-promoted calcium release from rat liver microsomal vesicles could be attributed to a GTP-dependent vesicle fusion. We have studied GTP-induced fusion of microsomal vesicles from rat exocrine pancreas using light scatter and fluorescence dequenching methods. In the presence of PEG (3%), GTP (10 μM) induced a decrease in light scatter and an increase in fluorescence in the fluorescence dequenching assay (GTP-effect) indicating fusion of the vesicles. Guanosine 5'-O-(3-thiotriphosphate) (10 μM) had no effect on its own and inhibited the GTP-induced signals. Preincubation of the vesicles with adenosine triphosphate (ATP) (4 mM) increased the GTP-effect by 80%. whereas bafilomycin B1, a specific inhibitor of vacuolar type H+-ATPases, and the protonophore CCCP (10 μM) inhibited only the ATP-dependent part of the GTP-effect. Inhibitors of the vacuolar type H+ -ATPase, which are also SH-alkylating reagents such as N-ethylmaleimid (100 μM) and the tyrosine-,cysteinc- and lysine-reactive reagent 7-chloro-4-nitrobenz-2-exa-1,3-diazole (10 μM) [2,3j. abolished the GTP-effect in the absence or presence of ATP. We conclude that GTP induces fusion of pancreatic microsomes which is increased by an H+ gradient established by a vacuolar type H+-ATPase.