Fig. 7.
Model of long-lasting suppression of L-current induced by D2 receptor-triggered interruption of positive feedback between L-channel activity and α1D gene expression. See Discussion for detailed explanation. Dopamine occupation of D2 receptors induces hyperpolarization and inhibition of spontaneous action potential activity (both indicated by line drawings labeled membrane potential). Haloperidol antagonizes activation of D2 receptors by endogenous dopamine, thus allowing spontaneous action potential firing. L- and P/Q-channels are activated by the depolarization of action potentials. L-channel activity triggers both secretion and α1D gene expression. P/Q-channels may also trigger secretion in melanotropes.