Fig. 6.

Inhibition of L-channels, but not P/Q-channels, mimics and occludes D2 receptor-induced downregulation of α_1D mRNA. α_1D mRNA levels in control and quinpirole-treated melanotropes cultured for 4 d in control media (No blockers; n = 15) or in the absence or presence of the indicated Ca²⁺ channel blockers (n = 3 in all cases). ns, Not statistically significant. The dashed line indicates the level of α_1D mRNA in quinpirole-treated cells cultured in the absence of Ca²⁺ channel blockers. Note that the L-channel inhibitor nimodipine mimics and occludes the effect of the D2-receptor agonist quinpirole. In contrast, P/Q-channel blockers have no effect.