Open AccessCharacterization of Ca2+ fluxes in rat liver plasma-membrane vesicles
Author(s) -
Catherine Dargemont,
Mauricette Hilly,
M Claret,
JeanPierre Mauger
Publication year - 1988
Publication title -
biochemical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.706
H-Index - 265
eISSN - 1470-8728
pISSN - 0264-6021
DOI - 10.1042/bj2560117
Subject(s) - vesicle , efflux , chemistry , cytosol , membrane , biophysics , biochemistry , calcium , chromatography , biology , enzyme , organic chemistry
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.