title: Evidence for a GTP-dependent increase in membrane permeability for calcium in NG108-15 microsomes.
abstract: The effect of GTP on Ca2+ uptake and release was studied in a microsomal fraction isolated from neuroblastoma x glioma hybrid NG108-15 cells. GTP did not alter the ATP-dependent initial uptake of Ca2+ but markedly enhanced the efflux of Ca2+ from microsomes. GTP-dependent Ca2+ release requires the presence of millimolar concentration of Mg2+. The effect of GTP was not mimicked by other nucleotides and was competitively blocked by the thiophosphate analogue of GTP, GTP gamma S but not by the non-hydrolyzable nucleotide GMP-PNP. Addition of an inhibiting concentration of GTP gamma S after completion of GTP-induced calcium release did not result in a re-uptake of Ca2+, showing the irreversibility of the releasing effect of GTP. Our data are consistent with the hypothesis of Ca2+-dependent GTP-induced opening of a channel responsible for vectorial transport of Ca2+ ions from one intracellular compartment to another. A model is proposed suggesting that the GTP-binding protein is a GTP-specific diacylglycerol kinase.
authors.affiliation: Laboratory of Biochemistry, National Cancer Institute, Bethesda, MD 20892.
authors.forename: T
authors.initials: T
authors.lastname: Jean
authors.forename: L A
authors.initials: LA
authors.lastname: Heppel
authors.forename: C B
authors.initials: CB
authors.lastname: Klee
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D005910:Glioma; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D006822:Hybrid Cells / Q000378:metabolism; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D009447:Neuroblastoma; D010070:Oxalates / Q000494:pharmacology; D051381:Rats
chemical_list: D010070:Oxalates; D000001:Calcimycin; D006160:Guanosine Triphosphate; D008274:Magnesium; D002118:Calcium