Fig. 5.

Saturation isotherms for the high-affinity Na⁺-dependent transport of glutamate in cortical (a), hippocampal (b), and striatal (c) synaptosomes prepared from end-stage G93A transgenic rats and age-matched controls. Glutamate uptake into P2 synaptosomal fractions was measured as described in Materials and Methods for the estimation of the kinetic parametersK_m and V_max. Initial rates of Na⁺-dependent glutamate uptake were expressed as picomoles per minute per milligram of synaptosomal protein after subtraction of the uptake observed in the absence of extracellular Na⁺ (equimolar replacement of NaCl with choline chloride). Kinetic constants K_mand V_max were estimated from the saturation isotherm using the Michaelis-Menten equation and are presented in Table3. Data represent mean ± SEM values from three independent experiments.