Endogenous reactive oxygen species modulates voltage-gated sodium channels in dorsal root ganglia of rats

Wang HJ, Li YL, Zhang LB, Zucker IH, Gao L, Zimmerman MC, Wang W. Endogenous reactive oxygen species modulates voltage-gated sodium channels in dorsal root ganglia of rats. J Appl Physiol 110: 1439-1447, 2011. First published February 3, 2011; doi: 10.1152/japplphysiol.01409.2010.-We recently reported that reactive oxygen species (ROS) plays an excitatory role in modulation of the exercise pressor reflex (EPR) in normal rats. In this study, we further tested two independent hypotheses: 1) ROS interacts with EPR-related ionotropic receptors such as the purinergic receptors (P-2) and transient receptor potential vanilloid 1 receptors (TRPV1) to indirectly modulate the EPR function; 2) ROS directly affects excitability of muscle afferents by modulating the voltage-gated sodium (Na-v) channels. To test the first hypothesis, we performed animal experiments to investigate the effect of the SOD mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-oxyl (Tempol) on the pressor response to hindlimb intra-arterial (IA) injection of either alpha,beta-methylene ATP (a P-2X agonist) or capsaicin (a TRPV1 agonist) in decerebrate rats. To test the second hypothesis, we used the patch-clamp technique to determine the effect of ROS on Nav channels on the soma of muscle afferents. We also performed local microinjection of a sodium channel blocker, tetrodotoxin (TTX), into ipsilateral L4/L5 dorsal root ganglia (DRGs) to investigate whether the blockade of Na-v channels by TTX affects the EPR function. We found that Tempol did not affect the pressor response to injection of either capsaicin or alpha,beta-methylene ATP but significantly decreased the Nav current in small and medium-sized 1,1=-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-labeled DRG neurons. A membrane-permeant superoxide dismutase, polyethylene glycol (PEG)-SOD, had an effect on the Nav current in these neurons similar to that of Tempol. Microinjection of TTX into L4/L5 DRGs dramatically attenuated the pressor response to static contraction induced by electrical stimulation of L4/L5 ventral roots. These data suggest that ROS modulates the EPR by affecting the activity of the Nav channels on muscle afferents.