The mechanism of action of GTP on Ca2+ efflux from rat liver microsomal vesicles. Measurement of vesicle fusion by fluorescence energy transfer.
1. GTP-promoted fusion between microsomal vesicles was studied by using fluorescence-resonance-energy transfer between the fluorescent membrane probes octadecanoyl-aminofluorescein and octadecyl-rhodamine. 2. The fluorescence increase after GTP addition does not require the presence of ATP, is unaffected by changes in free [Ca2+] in the range 10 microM-1 nM, but requires Mg2+, although higher Mg2+ concentrations are inhibitory. 3. In terms of requirements for poly(ethylene glycol), dependence on GTP concentration and inhibition by high Mg2+ concentrations, there is excellent correlation between rate of increase in fluorescence and rate of GTP-promoted Ca2+ efflux measured under Ca2+ transport conditions. 4. The observations support our previous conclusions that GTP-induced membrane fusion plays a major role in causing GTP-promoted Ca2+ efflux from microsomal vesicles.
Comerford
J G
JG
School of Biological Sciences, University of East Anglia, Norwich U.K.
Dawson
A P
AP
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D013050:Spectrometry, Fluorescence
D011092:Polyethylene Glycols; D006160:Guanosine Triphosphate; D008274:Magnesium; D002118:Calcium