Activation of TRPC Channels Contributes to OA-NO2-induced Responses in Guinea-pig Dorsal Root Ganglion Neurons

Effects of nitro-oleic acid (OA-NO2) on TRP channels were examined in guinea-pig dissociated dorsal root ganglia (DRG) neurons using calcium imaging and patch clamp techniques. OA-NO2 increased intracellular Ca(2+) in 60-80% DRG neurons. 1-Oleoyl-2acetyl-sn-glycerol (OAG), a TRPC agonist, elicited responses in 36% of OA-NO2-sensitive neurons while capsaicin (TRPV1 agonist) or allyl-isothiocyanate (AITC, TRPA1 agonist) elicited responses in only 16% and 10%, respectively, of these neurons. A TRPV1 antagonist (diarylpiperazine, 5 μm) in combination with a TRPA1 antagonist (HC-030031, 30 μm) did not change the amplitude of the Ca(2+) transients or percentage of neurons responding to OA-NO2; however, a reducing agent DTT (50 mm) or La(3+) (50 μm) completely abolished OA-NO2 responses. OA-NO2 also induced a transient inward current associated with a membrane depolarization followed by a prolonged outward current and hyperpolarization in 80% of neurons. The reversal potentials of inward and outward currents were approximately -20 mV and -60 mV, respectively. Inward current was reduced when extracellular Na(+) was absent, but unchanged by niflumic acid (100 μm), a Cl(-) channel blocker. Outward current was abolished in the absence of extracellular Ca(2+) or a combination of two Ca(2+)-activated K(+) channel blockers (iberiotoxin, 100 nm and apamin, 1 μm). BTP2 (1 or 10 μm), a broad spectrum TRPC antagonist, or La(3+) (50 μm) completely abolished OA-NO2 currents. RT-PCR performed on mRNA extracted from DRGs revealed the expression of all seven subtypes of TRPC channels. These results support the hypothesis that OA-NO2 activates TRPC channels other than the TRPV1 and TRPA1 channels already known to be targets in rat and mouse sensory neurons and challenge the prevailing view that electrophilic compounds act specifically on TRPA1 or TRPV1 channels. The modulation of sensory neuron excitability via actions on multiple TRP channels can contribute to the anti-inflammatory effect of OA-NO2.