Calcium-dependent release of endogenous glutamate from vascularly perfused rat stomach in vitro

To investigate a possible physiological role for glutamate in the stomach, release of endogenous glutamate from an isolated vascularly-perfused rat stomach preparation was studied. Glutamate was measured by the bioluminescence assay method. High concentrations of KCI (30-75 mM) induced a dose-dependent release of glutamate. This KCI-induced release of glutamate was abolished in calcium-free medium containing ethylene glycol bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). Electrical stimulation of the vagus nerves also induced a release of glutamate. This vagal stimulation-induced release of glutamate was abolished by both calcium removal and tetrodotoxin (TTX). Amounts of 13 other amino acids in the medium, detectable by the automatic amino-acid analyzer, were not significantly affected by both high-K+ and the vagal stimulation. These results provide additional evidence that glutamate probably serves as a neurotransmitter in the stomach.