Ganglion-Specific Sensitivity of P2X3 Receptors to Leu-Enkephalin

In this study, several properties of modulation of P2X3 currents by an endogenous opioid, leu-enkephalin (LEK), in neurons of the dorsal root and nodose ganglia (DRGs and NGs, respectively) were compared. P2X3-mediated currents were recorded using a patch-clamp technique in the whole-cell configuration. P2X3 receptors in DRG neurons were found to be more sensitive to LEK application compared to NG neurons; complete suppression of the corresponding currents required lower concentrations of LEK and rose more quickly. Short-term preapplication of naloxone (a nonselective opioid receptor antagonist) on NG neurons did not alter the effect of the tested opioid on P2X3 currents, while it dramatically enhanced LEK-induced inhibition in DRG neurons. This fact may be indicative of the existence of specific intracellular pathways involved in opioid-induced modulation of P2X3 receptors of different peripheral ganglia in vertebrates.