Dynorphin reduces voltage-dependent calcium conductance of mouse dorsal root ganglion neurons

Dynorphin A (DYN) (1 microM) decreased somatic calcium-dependent action potential (CAP) duration of a portion of dorsal root ganglion (DRG) neurons in a naloxone reversible manner. Responses to DYN differed from responses to Leu-enkephalin in that only DYN decreases of somatic CAP duration were associated with decreased action potential after hyperpolarization and persisted after intracellular injection of the potassium channel blocker cesium. While Leu-enkephalin at 10 microM did not affect somatic CAP duration of DRG neurons impaled with cesium-filled micropipettes, dynorphin A (1-8), dynorphin B, and beta-neoendorphin were effective at 1 microM. During single electrode voltage clamp, DYN decreased inward current in a portion of DRG neurons under conditions that predominately isolated calcium current. Leak current was unaffected by dynorphin A. Therefore, we suggest that DYN decreases voltage-dependent calcium conductance. The action on calcium conductance appears specific for opioids with affinity for kappa-receptors.