The neuropharmacological study of endogenous glutamate release from the stomach

为了探讨谷氨酸在胃中可能的生理作用，研究了内源性谷氨酸在离体大鼠血管灌注胃制剂中的释放。用生物发光法测定谷氨酸。高浓度KCI （30-75mM）诱导谷氨酸释放呈剂量依赖性。这种kci诱导的谷氨酸释放在含EGTA的无钙培养基中被消除。对迷走神经的电刺激也会引起谷氨酸的释放。这种迷走神经刺激诱导的谷氨酸释放被钙去除和河豚毒素（TTX）所消除。另外13种氨基酸在高k +和迷走神经刺激下的含量，经自动氨基酸分析仪检测均无显著影响。在接下来的系列中，我们研究了钙通道亚型介导的特性。内源性谷氨酸从胃释放。50 mM KCI诱导的谷氨酸释放被P/ q型钙通道拮抗剂omega-agatoxin IVA和L型钙通道拮抗剂isradipine显著抑制。ω - concontoxin GVIA （N型钙通道拮抗剂）和氟桂利嗪（非选择性t型钙通道拮抗剂）没有效果。与谷氨酸的情况相反，omega- concontoxin GVIA诱导了胃去甲肾上腺素释放的显著抑制。omega-agatoxin IVA加isradipine联合治疗对谷氨酸释放有明显的协同抑制作用。然而，这种抑制作用远远小于镉的抑制作用。这些结果为谷氨酸可能在胃中作为一种神经递质提供了额外的证据，并提示P/Q和L型钙通道共存调节胃谷氨酸的释放。此外，除了P/Q和L型通道外，可能还有未知的钙通道参与胃中谷氨酸的释放。

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.