Properties of calcium channels coupled to endogenous glutamate release from the vascularly perfused rat stomach in vitro.
We have demonstrated that both high-K+ and electrical stimulation of the vagus nerves release endogenous glutamate from the vascularly-perfused rat stomach in a calcium-dependent manner. In the present study, we examined properties of calcium channel subtypes mediating endogenous glutamate release from the stomach. Application of 50 mM KCl elicited a release of glutamate, and this release was abolished in calcium-free medium. The 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. The present results 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.
Okuma
Y
Y
Department of Pharmacology, Kochi Medical School, Nankoku, Japan.
Yokotani
K
K
Murakami
Y
Y
Osumi
Y
Y
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005753:Gastric Mucosa / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D017275:Isradipine / Q000494:pharmacology; D008297:Male; D010477:Perfusion; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013111:Spider Venoms / Q000494:pharmacology; D013270:Stomach / Q000098:blood supply / Q000187:drug effects; D020867:omega-Agatoxin IVA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D018698:Glutamic Acid; D011188:Potassium; D017275:Isradipine