Sodium dependence of GABA transport in rat hypothalamic synaptosomes

The sodium dependence of gamma-aminobutyric acid (GABA) uptake has been studied in rat hypothalamic synaptosomes, and the results compared to previous studies in cortical synaptosomes. Initial velocity of GABA uptake was measured as a function of both GABA and sodium concentration, and these data were fitted to the rate equation for each of several plausible models. The minimal best-fit model was found to be identical to that for cortical synaptosomes. However, the constants which quantitate the model were found to differ for hypothalamus and cortex. As a result, uptake at any combination of [Na] and [G] in hypothalamic synaptosomes is approximately double that in cortical synaptosomes. The rate equation for the minimal best-fit model was utilized to define and compute certain parameters which are useful in comparing transport mechanisms (Vmax, Va, Kt, Jm, and k Na). In all cases, differences were found between hypothalamus and cortex.