Characterization of D‐Aspartic Acid Uptake by Rat Hippocampal Slices and Effect of Ischemic Conditions

: The cellular uptake of D‐aspartic acid (D‐Asp) as a model compound for glutamic acid transport was studied in rat hippocampal slices. 1‐Asp is accumulated by both Na+‐dependent and Na+‐independent processes in hippocampal slices, and both processes are dependent on temperature. The Na+‐dependent uptake is assumed to be high in affinity (apparent Km = 0.17 mM), but low in capacity, whereas the Na+‐independent uptake is much lower in affinity (Km = 2.86 mM), but higher in capacity. l‐Aspartic acid, l‐glutamic acid, dihydrokainic acid, and threo‐3‐hydroxy‐DL‐aspartic acid markedly inhibited the uptake of D‐Asp with Na+ in the medium, whereas D‐glutamic acid, glycine, and l‐lysine had no significant effect. The Na+‐dependent uptake of D‐Asp was significantly reduced under “hypoglycemic,”“anoxic,” and “ischemic” conditions, whereas the Na+‐independent uptake was unaffected. Metabolic inhibitors such as NaCN and ICH2COOH significantly inhibited the Na+‐dependent uptake, but not the Na+‐independent uptake. These results suggest that the Na+‐dependent component of D‐Asp transport in rat hippocampal cells is inactivated under ischemic conditions, whereas the Na+‐indepen‐dent component is unaffected.