DIFFERENTIAL-EFFECTS OF CALCIUM-CHANNEL ANTAGONISTS ON TITYUSTOXIN AND OUABAIN-INDUCED RELEASE OF [H-3] ACETYLCHOLINE FROM BRAIN CORTICAL SLICES

In this paper, the effect of calcium channel blockers on acetylcholine release induced by tityustoxin and ouabain in rat brain cortical slic es is described. Cadmium, a non-specific blocker of calcium channels, inhibited the release of ACh induced by tityustoxin. L-type calcium ch annel blockers (verapamil, nifedipine and diltiazen) had no effect on the release of ACh induced by tityustoxin. The release of ACh was also unaffected by nickel, a T-type calcium channel blocker, and the conot oxins GVIA and MVIIC, blockers of N and Q-type calcium channels. Agato xin IVA, a specific blocker of the P-type calcium channel, inhibited t he release of ACh induced by tityustoxin by 50%. The spontaneous relea se of ACh as well as ouabain-induced release of ACh was unaffected by any of the calcium channel blockers studied. It is concluded that ACh release induced by tityustoxin is mediated by Ca2+ influx via P-type c alcium channels.