The effect of arachidonic acid and free fatty acids on vesicular uptake of glutamate and γ-aminobutyric acid

The manner in which arachidonic acid and other free fatty acids influence the vesicular uptake of glutamate and γ-aminobutyric acid (GABA) has been investigated. The cis-polyunsaturated fatty acid arachidonic acid (20:4), eicosapentanoic acid (20:5) and linolenic acid (18:3) at 150 nmol/mg protein (50 μM) inhibited the vesicular uptake of glutamate and GABA more than 70%. Reduced inhibition of vesicular uptake was seen with the cis-monounsaturated fatty acid oleic acid (18:1) and the trans-mono-unsaturated fatty acid elaidic acid (18:1). The saturated fatty acids stearic acid (16:0) and arachidic acid (20:0) had no significant effect on the uptake. The inhibition of vesicular uptake by arachidonic acid was prevented by the addition of fatty acid free bovine serum albumin. Arachidonic acid inhibited in a dose-dependent manner the generation of the transmembrane pH gradient of the synaptic vesicles. This inhibition was proportional to the inhibition of the vesicular uptake of glutamate and GABA. The saturated fatty acid arachidic acid showed no inhibition of ΔpH generation. Arachidonic acid at 200 nmol/mg of protein did not increase the uptake-independent leakage of glutamate and GABA from the vesicles, showing that the effect of arachidonic acid is not caused by an unspecific detergent effect. These results suggest that arachidonic acid and other polyunsaturated fatty acids are acting like proton-ionophores on the vesicular uptake of these neurotransmitters. This finding may have implications for the increased fatty acid concentration during pathological conditions like ischemia and in long term potentiation.