Norepinephrine inhibits calcium-dependent potentials in rat sympathetic neurons.

Norepinephrine reversibly antagonizes three calcium-dependent potentials recorded from rat postganglionic neurons. Norepinephrine inhibits the development of a shoulder on the aciton potential, the magnitude of the hyperpolarizing afterpotential, and the rate of rise and amplitude of the calcium spike. The action of norepinephrine is antagonized by the alpha-adrenergic antagonist phentolamine, but not by MJ 1999, a beta-adrenergic antagonist. These results suggest that activation of an alpha-adrenergic receptor may antagonize a voltage-sensitive calcium current.