Voltage-activated calcium channels involved in veratridine-evoked [3H]dopamine release in rat striatal slices

The present study explored the role of different sub-types of voltage-activated Ca2+ channels (VACCs) in mediating veratridine-evoked [3H]dopamine (DA) release from rat striatal slices. The release of [3H]DA evoked by veratridine (25 microM) decreased by 50.6+/-2.9% (n=8) in the absence of calcium and was completely abolished by 1 microM tetrodotoxin. The L-type Ca2+ channel blockers nifedipine (10 microM), nitrendipine (10 microM), diltiazem (10 microM) and verapamil (10 microM) did not modulate this release. Similarly, [3H]DA release was affected neither by the N-type VACC blocker omega-conotoxin-GVIA (1 microM) nor by the selective P-type channel blockers omega-agatoxin-IVA and omega-agatoxin-TK at low nM concentrations (30 nM), indicating no involvement of N- and P-type Ca2+ channels. In contrast, higher concentrations of omega-agatoxin-IVA that would also inhibit Q-type VACCs, blocked the release of [3H]DA by 27.9+/-8.1% (n=5) and 37.5+/-13.6% (n=3) at 0.3 and 1 microM, respectively. In addition, application of the Q-type Ca2+ channel blocker omega-conotoxin-MVIIC (0.01-3 degrees M) reduced [3H]DA release in a concentration-dependent manner, with maximum inhibition of 35.3+/-4.1% at 3 microM (n=5). On the basis of these results, it is concluded that the Ca2+ channels that participate in veratridine-evoked [3H]DA release are Q-type Ca2+ channels.