A comparison of high affinity synaptosomal uptake of d-aspartate in rat and human brain

Synaptosomes were prepared from frozen post mortem human brain and from fresh rat brains. These preparations were used to compare the pharmacological properties of the sodium dependent, high affinity, excitatory amino acid uptake sites in these species, using [(3)H]d-aspartate as the ligand. The kinetic parameters for the human and rat uptake sites were: K(m) = 9.14 +/- 1.34 and 6.71 +/- 0.89 ? M; and V(max) = 1.12 +/- 0.16 and 5.28 +/- 0.70 nmol/min/mg protein respectively. Both sites showed similar pharmacological profiles for the inhibition of d-aspartate uptake when a series of structural analogues were used. Detailed kinetic analyses were performed at a number of sodium concentrations to determine the sodium requirement of the uptake sites. The results in both species were consistent with a coupling ratio of one sodium ion to one d-aspartate molecule. These results demonstrate the feasibility of using synaptosomal d-aspartate uptake as a presynaptic marker of excitatory amino acid neurons in human brain.