A comparison of sodium dependent GABA transport in cortical synaptosomes from Long-Evans and Sprague-Dawley rats

Summary

The sodium dependent, high affinity transport of GABA has been studied in cortical synaptosomes from Sprague-Dawley (SD) rats and the results compared to previous results from Long-Evans (LE) rats. Initial velocity of uptake was measured as a function of both GABA and sodium concentration. These data were then fitted to the rate equation for the model which was found to give minimal best fit to similar data from Long-Evans animals. An excellent fit was obtained; the average per cent error between experimental data and model predictions is only 2.55%. No simplification of the model could be made without lessening the goodness of fit. Thus there are no fundamental differences between the two groups in the mechanism by which carrier, sodium, and GABA interact in the process of transport.

Although the same model was found to fit the velocity data from both groups of animals, there are differences in the constants which quantitate the model. As a consequence, uptake at a given sodium and GABA concentration may be different for the two groups. The rate equation for the model permits certain functions to be defined in terms of dissociation and translocation constants, GABA, sodium, and total carrier concentrations. The best fit constants were used to calculate these functions, which were then utilized to demonstrate further the quantitative similarities and differences in the transport mechanism in the two groups of animals. In general, those parameters reflective of carrier affinity for sodium or GABA indicated greater affinities in the LE group, while those parameters reflective of carrier concentration or rate constants indicated greater carrier concentration, rate constants, or both, for SD animals.