Opioid Peptides Selective for Mu- and Delta-opiate Recep- Tors Reduce Calcium-dependent Action .potential Dura- Tion by I N C ~ S I N G Potassium Conductance

We suggest that both muand delta-opiate receptors on dorsal root ganglion neuron somata are coupled to voltageand/or calcium-dependent potassium channels since opioid peptide decreases of calciumdependent action potential duration were: (1) not associated with a change of resting membrane potential or conductance; (2) accompanied by an increase in action potential after-hyperpolarization, and (3) blocked by intracellular injection of the potassium channel blocker cesium [18]. In contrast, norepinephrine [4l and cadmium [9], which have been reported to act on voltage-dependent calcium rather than potassium channels, shortened action potential duration and decreased afterhyperpolarization amplitude, an action not blocked by intracellular iontophoresis of cesium.