Kandasamy, S. B. Possible Involvement of L-Type Voltage-Gated Calcium Channels in Release of Dopamine in the Striatum of Irradiated Rats.

The object of this study was to determine the effect of exposure to γ radiation on potassium chloride (KCl)-stimulated release of dopamine (DA) in the striatum of the rat. In addition, the effect of some calcium channel blockers [nicardipine, a blocker of the L-type voltage-gated N-type VGCC; Ω-agatoxin TK, a selective blocker of P-type VGCC; and nickel chloride (NiCl₂), which preferentially blocks the T-type VGCC] on KCl-stimulated release of DA in the striatum in sham-irradiated and irradiated rats was determined. Exposure of rats to 1–10 Gy ⁶⁰Co γ rays had no significant effect on KCl-stimulated release of DA in the striatum in comparison to sham-irradiated animals. Administering 100, 300 and 500 nM of Ω-agatoxin TK or 50, 100 and 200 nM of Ω-conotoxin GVIA significantly decreased the release of DA stimulated by KCl in both irradiated and sham-irradiated animals in a dose-dependent manner. However, 10, 30 and 50 μM of nicardipine decreased the release of DA in irradiated animals but not in sham-irradiated animals. It is unknown why doses of 5–20 μM NiCl₂ had no effect on the release of DA in sham-irradiated and irradiated animals. The results demonstrate that the doses of radiation used in this study had no effect on release of DA in the striatum. Multiple calcium channel types coexist to regulate release of DA. P- and N-type VGCCs are involved in release of DA in sham-irradiated and irradiated animals, whereas only L-type VGCCs are involved in release of DA in irradiated animals.