BARIUM ELICITS REVERSAL OF LOW-CONCENTRATION ETORPHINE-INDUCED DECREASE OF POTASSIUM CONDUCTANCE IN CULTURES OF DISSOCIATED DORSAL MOT GANGLION NEURONS

Etorphine is an non-selective opioid receptor agonist with very potent analgesic effect. Low concentrations (<nM) of most opioid receptor ag onists decrease the K+ conductance (g(K)) in cultures of dissociated m ouse dorsal root ganglion neurons regardless of the presence of Ba2+ H owever, low concentrations of etorphine, in contrast to all other opio ids tested, decreased g(K) only in the absence of Ba2+. In the presenc e of Ba2+, pM-nM etorphine elicited dose-dependent increases, instead of decreases in g(K). Higher concentrations of etorphine (>nM) not onl y increased g(K) but, in addition, appreciably increased a delayed-ons et inward Ca2+ current during pulsed depolarisation regardless of the presence of Ba2+.