title: GTP-mediated Ca2+ release in rough endoplasmic reticulum. Correlation with a GTP-sensitive increase in membrane permeability.
abstract: Guanine nucleotides have been reported to stimulate reticular Ca2+ release. By using the structure-linked latency of microsomal mannose-6-phosphate phosphatase as an index of microsomal permeability [Arion, Ballas, Lange & Wallin (1976) J. Biol. Chem. 251, 4901-4907], the effects of GTP on Ca2+ release and membrane permeability were compared in liver microsomes. In a stripped rough-microsome preparation, GTP caused a dose-dependent increase in mannose 6-phosphate permeability. Half-maximal and maximal effects were observed at 3 microM- and 10 microM-GTP respectively. The time course of the change in membrane permeability coincided with the time course of GTP-dependent Ca2+ release. This increase in microsomal permeability displayed positive to-operativity with respect to GTP (Hill coefficient = 1.8). By analogy to the GTP-dependent Ca2+ release process, guanosine 5'-[gamma-thio]triphosphate and guanosine 5'-[beta gamma-imido]-triphosphate inhibited the ability of GTP to alter microsomal permeability, but were without effect when added alone. In the presence of 50 microM-GTP, complete inhibition of the GTP-dependent increase in microsomal permeability was achieved with 10 microM-guanosine 5'-[gamma-thio]triphosphate, whereas a 25% inhibition was observed with 10 microM-guanosine 5'-[beta gamma-imido]triphosphate. In contrast with previous observations in crude microsomal preparations, GTP-dependent Ca2+ release in the stripped rough-microsome preparation did not require the addition of poly(ethylene glycol), although the latter did stimulate the rate of Ca2+ release. The ability of GTP to alter microsomal permeability was blocked by prior treatment with the thiol reagent p-hydroxymercuribenzoate; complete inhibition was observed after a 10 min exposure to 50 microM. Inhibition was reversed by subsequent treatment with dithiothreitol. The marked similarities between the two GTP-sensitive processes indicate that they may function via the same mechanism.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104.
authors.forename: C V
authors.initials: CV
authors.lastname: Nicchitta
authors.forename: S K
authors.initials: SK
authors.lastname: Joseph
authors.forename: J R
authors.initials: JR
authors.lastname: Williamson
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000493:pharmacokinetics*; D006902:Hydroxymercuribenzoates / Q000493:pharmacokinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009711:Nucleotides / Q000493:pharmacokinetics; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D011092:Polyethylene Glycols / Q000493:pharmacokinetics; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship
chemical_list: D006902:Hydroxymercuribenzoates; D009711:Nucleotides; C030601:4-hydroxymercuribenzoate; D011092:Polyethylene Glycols; D006160:Guanosine Triphosphate; C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; D002118:Calcium