Sodium dependence of high affinity glutamic acid transport in cortical synaptosomes?a comparison of Long-Evans and Sprague-Dawley rats

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Abstract
The sodium dependence of high affinity glutamic acid transport has been studied in cortical synaptosomes from Sprague‐Dawley rats and compared to previous studies with Long‐Evans rats. Initial velocity of uptake was measured as a function of both glutamate and sodium concentration, and the data fitted to the rate equations for the same set of models that was utilized in the Long‐Evans studies. The minimal best‐fit model was found to be identical to that found previously for Long‐Evans animals. Thus there are no fundamental differences in the basis of the sodium dependence of high affinity glutamate transport between the two groups. However, since the constants describing the best fit model are different for the two groups of animals, there are quantitative differences in the transport mechanism between the two groups. The rate equation for the minimal best‐fit model permits certain functions to be defined in terms of dissociation and translocation constants, substrate, sodium, and total carrier concentrations. These functions were calculated and then utilized to demonstrate the quantitative differences in the transport mechanism in the two groups.