Modulation of sensory neuron potassium conductances by anandamide indicates roles for metabolites.

BACKGROUND AND
PURPOSE: The endogenous cannabinoid anandamide (AEA) acts at cannabinoid (CB(1)) and vanilloid (TRPV(1)) receptors. AEA also shows antinociceptive properties; although the underlying mechanism for this is not fully understood, both CB(1) and TRPV(1) may be involved. Voltage-activated Ca(2+) channels in rat-cultured dorsal root ganglion (DRG) neurons are modulated by AEA. However, AEA in different populations of neurons enhanced or attenuated KCl-evoked Ca(2+) influx; these effects were linked with soma size. The aim of this study was to determine how AEA or its metabolites might produce these variable responses. EXPERIMENTAL APPROACH: The whole cell patch-clamp technique and fura-2 Ca(2+) imaging were used to characterize the actions of AEA on action potential firing and voltage-activated K(+) currents and to determine whether AEA metabolism plays any role in its effects on cultured DRG neurons. KEY
RESULTS: AEA attenuated multiple action potential firing evoked by 300 ms depolarizing current commands in a subpopulation of DRG neurons. Application of 1 microM AEA attenuated voltage-activated K(+) currents and the recovery of KCl-evoked Ca(2+) transients. The insensitivity of these responses to the CB(1) receptor antagonist rimonabant (100 nM) and preincubation of DRG neurons with pertussis toxin suggested that these actions are not CB(1) receptor-mediated. Preincubating DRG neurons with the fatty acid amide hydrolase (FAAH) inhibitor phenylmethylsulphonyl fluoride (PMSF) attenuated the inhibitory actions of AEA on K(+) currents and Ca(2+) influx. CONCLUSION AND IMPLICATIONS: These data suggest that the products of AEA metabolism by FAAH contribute to the attenuation of K(+) conductances and altered excitability of cultured sensory neurons.