CHARACTERIZATION AND PH-DEPENDENCE OF L-GLUTAMATE TRANSPORT IN SARCOLEMMAL VESICLES FROM RAT HEARTS

Transport of L-glutamate in purified sarcolemmal vesicles from rat hea rt was Na+ dependent and characterized by an apparent affinity value o f 0.149 +/- 0.04 mM (n = 6). Na+ binding to the carrier was not very s pecific, since an inwardly directed K+ gradient could also increase ve sicular uptake of L-glutamate. Uptake of L-glutamate into sarcolemmal vesicles was inhibited by L-aspartate and L-cysteinate. These characte ristics of glutamate uptake are typical of transport via system X(AG)( -). Acidification of either the intravesicular or the extrave sicular space led to a significant increase in L-glutamate transport. This inc rease was more pronounced when the intravesicular space had been acidi fied. Thus intracellular acidosis of hypoxic or ischemic myocardium is directly linked to an increased uptake of glutamate.