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.