Effects of meconic and comenic acids on slow sodium channels of secondary neurons

Effects of comenic and meconic acids on cultured dorsal root ganglion cells were investigated by the whole-cell patch clamp technique. The acids, having a well-known antiinflammatory and antibacterial action, decreased effective charge transfer in the activation gating system of TTX-resistant (slow) sodium channels in a dose-dependent manner. The effects were described by Hill's equation. The dissociation constant and Hill coefficient values were K(D) = 100 nM and X = 0.5 (for comenic acid) and K(D) = 10 nM and X = 0.34 (for meconic acid). The nonspecific antagonist of opioid receptors naltrexone totally blocked the effects. We suggest that the acids studied activate a subpopulation of opioid receptors negatively coupled to TTXr sodium channels.