(+/-)-beta-Parachlorophenylglutamate selectively enhances the depolarizing response to L-homocysteic acid in neocortical neurons of the rat: evidence for a specific uptake system.

The effect of (+/-)-beta-parachlorophenylglutamate (CP) on depolarizations induced by iontophoretically applied L-glutamate, L-aspartate, L-homocysteate (L-HCA) and D-HCA was investigated in neurons of the rat neocortex in vitro. CP, a reported blocker of amino acid uptake, strongly enhanced L-HCA responses whereas responses to the other amino acids remained little affected. This action was observed irrespective of whether CP was administered iontophoretically or pneumatically from micropipettes. CP (5 mM) administered alone had no effect on membrane potential. These findings suggest the existence of a specific uptake system for L-HCA providing further evidence in favour of a possible function of L-HCA as an endogenous ligand for the N-methyl-D-aspartate receptor in the rat neocortex.