Modulation of voltage-dependent potassium currents by opiates in facial motoneurons of neonatal rats

We examined the modulation of rat facial motoneurons (FMNs) by opiates in a slice preparation (7-15 days old) using whole-cell patch clamp techniques. Although application of methionine enkephalin (ME) did not change the peak value of the transient outward current (A-current, IA). it reduced the persistent voltage-dependent K+ currents (IKs) in a dose-dependent manner. The reduction was antagonized by naloxone (40 muM). IKs were reduced only by mu-selective agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO, 2-121.6 muM). This reduction was antagonized by naloxone (40 muM) or the R-selective antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (CTOP, 1 muM). Agonists for other opiate receptors (delta- and kappa-opiate receptor) showed no effect on IKs. In accord with the effects on IKs, DAMGO (100 muM) prolonged the duration of the action potential evoked in Ca2+-free external solution containing 4-aminopiridine (1 mM). These results suggest that the activation of mu-opiate receptors contributes to signal transduction in FMNs primarily by modulating action potential duration. (C) 2003 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.