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KINETICS OF THE SODIUM‐DEPENDENT TRANSPORT OF GAMMA‐AMINOBUTYRIC ACID BY SYNAPTOSOMES
Author(s) -
Martin D. L.
Publication year - 1973
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.1471-4159.1973.tb04255.x
Subject(s) - sodium , kinetics , chemistry , cooperativity , potassium , aminobutyric acid , allosteric regulation , sodium channel , biophysics , biochemistry , enzyme , biology , receptor , organic chemistry , physics , quantum mechanics
The kinetics of transport of gamma‐aminobutyric acid [2,3‐ 3 H] by synaptosomes from rat brain was studied by means of a rapid filtration technique. The rate of uptake was proportional to the protein concentration over the range 0.05—0.2 mg of synaptosomal protein per ml. Although apparent allosteric kinetics were observed with sodium, transport followed simple saturation kinetics with respect to GABA and no heterotropic, cooperative effects of GABA on sodium on kinetics were observed. A minimum of three interacting sodium sites is suggested the basis of Hill plots of the sodium data. Both the apparent K m and V max for GABA were functions of the sodium ion concentration but the effect of sodium was considerably greater on V max than on the apparent K m The V max for GABA was 1.1 ± 0.5 nmol.min −1 mg −1 of protein at 95 m m sodium and decreased to 12 per Cent of this value at 19 m m sodium. The apparent K m for GABA increased from 4.0 ± 1.0 μ m at 95 m m sodium to 8.4 ± 2.0 μm at 19 m m sodium. Potassium was a noncompetitive inhibitor with respect to GABA and did not affect the apparent cooperativity observed with sodium. These findings are discussed in terms of models of GABA transport.