Neuronal and glial plasma membrane carrier-mediated uptake of l-homocysteate is not selectively blocked by β-p-chlorophenylglutamate

The proposed action of β-p-chlorophenylglutamate (chlorpheg) as a selective blocker of l-homocysteate uptake was studied in primary cultures of mouse brain neurons and astrocytes and in rat brain synaptosomes. The preparations were incubated with 1 μM to 10 mM l-homocysteate and d-aspartate in the absence and presence of 7.5 mM chlorpheg. In each preparation uptake of the two amino acids comprised a saturable uptake and a non-saturable (passive diffusion) component. l-Homocysteate was of at least 100-fold lower affinity than d-aspartate as a substrate for the amino acid transporter. Chlorpheg was shown to be essentially equieffective as a weak competitive inhibitor of only the saturable uptake of l-homocysteate and d-aspartate. It is concluded that chlorpheg is not a selective blocker of l-homocysteate uptake.