Barium elicits reversal of low-concentration etorphine-induced decrease of potassium conductance in cultures of dissociated dorsal root ganglion neurons.

Etorphine is an non-selective opioid receptor agonist with very potent analgesic effect. Low concentrations (< nM) of most opioid receptor agonists decrease the K+ conductance (gK) in cultures of dissociated mouse dorsal root ganglion neurons regardless of the presence of Ba2+ However, low concentrations of etorphine, in contrast to all other opioids tested, decreased gK only in the absence of Ba2+. In the presence of Ba2+, pM-nM etorphine elicited dose-dependent increases, instead of decreases in gK. Higher concentrations of etorphine (> nM) not only increased gK but, in addition, appreciably increased a delayed-onset inward Ca2+ current during pulsed depolarization regardless of the presence of Ba2+.