Characterization and pH dependence of L-glutamate transport in sarcolemmal vesicles from rat hearts.

Transport of L-glutamate in purified sarcolemmal vesicles from rat heart was Na+ dependent and characterized by an apparent affinity value of 0.149 +/- 0.04 mM (n = 6). Na+ binding to the carrier was not very specific, since an inwardly directed K+ gradient could also increase vesicular uptake of L-glutamate. Uptake of L-glutamate into sarcolemmal vesicles was inhibited by L-aspartate and L-cysteinate. These characteristics of glutamate uptake are typical of transport via system XAG-. Acidification of either the intravesicular or the extravesicular space led to a significant increase in L-glutamate transport. This increase was more pronounced when the intravesicular space had been acidified. Thus intracellular acidosis of hypoxic or ischemic myocardium is directly linked to an increased uptake of glutamate.