Characterization of Ca2+ fluxes in rat liver plasma-membrane vesicles.
Inside-out plasma-membrane vesicles isolated from rat liver [Prpic, Green, Blackmore & Exton (1984) J. Biol. Chem. 259, 1382-1385] accumulated a substantial amount of 45Ca2+ when they were incubated in a medium whose ionic composition and pH mimicked those of cytosol and which contained MgATP. The Vmax of the initial 45Ca2+ uptake rate was 2.9 +/- 0.6 nmol/min per mg and the Km for Ca2+ was 0.50 +/- 0.08 microM. The ATP-dependent 45Ca2+ uptake by inside-out plasma-membrane vesicles was about 20 times more sensitive to saponin than was the ATP-dependent uptake by a microsomal preparation. The 45Ca2+ efflux from the inside-out vesicles, which is equivalent to the Ca2+ influx in intact cells, was increased when the free Ca2+ concentration in the medium was decreased. The Ca2+ antagonists La3+ and Co2+ inhibited the 45Ca2+ efflux from the vesicles. Neomycin stimulated the Ca2+ efflux in the presence of either a high or a low free Ca2+ concentration. These results confirm that polyvalent cations regulate Ca2+ fluxes through the plasma membrane.
Dargemont
C
C
Unité de Recherches de Physiologie et Pharmacologie Cellulaire, Inserm U. 274, Université Paris-Sud, France.
Hilly
M
M
Claret
M
M
Mauger
J P
JP
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000493:pharmacokinetics*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009355:Neomycin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012503:Saponins / Q000494:pharmacology; D012964:Sodium / Q000493:pharmacokinetics
D007295:Inositol Phosphates; D012503:Saponins; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D009355:Neomycin; D002118:Calcium