|Budget Amount *help
¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1997 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1996 : ¥1,000,000 (Direct Cost : ¥1,000,000)
To investigate a possible physiological role of glutamate in the stomach, release of endogenous glutamate from an isolated vascularly perfused rat stomach preparation was studied. Glutamate was measured by bioluminescence assay method.
High concentration of KCI (30-75mM) induced a dose dependent release of glutamate. This KCI-induced release of glutamate was abolished in calcium-free medium containing 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 other 13 amino acids in the medium, detectable by the automatic amino acid analyzer, were not significantly affected by both high-K+and the vagal stimulation.
In the next series, we examined properties of calcium channel subtypes mediating.
endogenous glutamate release from the stomach. The 50 mM KCI elicited release of glutamate was significantly inhibited by both omega-agatoxin IVA,a P/Q-type calcium channel antagonist, and isradipine, an L type calcium channel antagonist. Omega-Conotoxin GVIA,an N type calcium channel antagonist and flunarizine, a nonselective T-type calcium channel antagonist were without effect. In contrast to this case of glutamate, omega-conotoxin GVIA induced a marked inhibition in the release of gastric noradrenaline. The combined treatment with omega-agatoxin IVA plus isradipine produced a marked synergistic inhibition of the glutamate release. This inhibition was, however, much less than that by cadmium. These results provide an additional evidence that glutamate probably serves as a neurotransmitter in the stomach, and suggest that P/Q and L type calcium channels coexist to regulate the release of gastric glutamate. Furthermore, it is possible that unidentified calcium channels other than P/Q and L type channels are also involved in the release of glutamate in the stomach.