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SODIUM‐INDUCED EFFLUX OF CALCIUM FROM BRAIN MICROSOMES
Author(s) -
Robinson J. D.
Publication year - 1969
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1969.tb06858.x
Subject(s) - efflux , calcium , sodium , oligomycin , chemistry , ouabain , microsome , biochemistry , incubation , atpase , in vitro , enzyme , organic chemistry
—1 A microsomal preparation from rat brain accumulated 45 Ca in the presence of ATP. The uptake of calcium was associated with a corresponding uptake of 32 P from [γ‐ 32 P]ATP, with a 32 P: 45 Ca molar ratio of about 0·65. 2 Microsomes that were first loaded with 46 Ca lost radioactivity during a subsequent incubation in the absence of ATP; efflux of previously accumulated 32 P (from ATP) corresponded with the calcium efflux. By contrast, the uptake of 14 C from [8‐ 14 C]ATP was far less than of 32 P, and the efflux did not follow calcium efflux. Thus the movement of 32 P probably represented the phosphate anion in association with calcium. Calcium efflux diminished with increasing pH up to 8·6. 3 Sodium specifically increased the rate of efflux of previously accumulated calcium. This sodium‐induced efflux was associated with a corresponding efflux of 32 P (from ATP) and had a pH optimum near 7·8. It was not accompanied by a change in the amount of retained adenine nucleotides nor in the pattern of ATP metabolites, and was unaffected by ouabain or oligomycin. 4 Low concentrations of certain sulphydryl inhibitors blocked the sodium‐stimulated efflux with little effect either on efflux in the absence of sodium or on 45 Ca accumulation. 5 Higher concentrations of these inhibitors, associated with an increase binding of the reagent, caused a generalized efflux of 45 Ca and an inhibition of accumulation. The lipid solubility of a series of mercurial reagents corresponded with efficacy in promoting efflux; this suggested that this second class of reactive sites lay within a lipoidal permeability barrier.