Nerve growth factor contributes augmented P2X3 expression of primary afferent neurons by femoral occlusion

Abstract

Femoral artery occlusion augments the reflex sympathetic nerve and pressor responses to muscle metabolites and to muscle contraction in rats. Also, P2X3 receptors contribute the metabolic component of the exercise pressor reflex. Thus, the purpose of this study was to examine if femoral occlusion alters expression of P2X3 in dorsal root ganglion (DRG) neurons and its responsiveness in rats. In addition, we examined role of nerve growth factor (NGF) in the levels of P2X3 proteins in sensory neurons. Our western blot results showed that 24hrs of femoral ligation increased the levels of P2X3 (optical density: 0.93±0.07 in control vs. 1.37±0.10 after occlusion, P<0.05). The fluorescence immunohistochemistry further demonstrated that the occlusion elevated P2X3 expression in DRG neurons (percentage of P2X3 positive cells: 33±3% in control vs.51±3% in occlusion, P<0.05). Furthermore, our results showed that responses of renal sympathetic nerve activity and blood pressure to stimulation of P2X were greater in occluded rats than in control rats by injection of α,β me-ATP into the arterial blood supply of hindlimb muscle. Finally, infusion of NGF in the hindlimb muscles of healthy rats increased P2X3 (optical density: 0.98±0.12 in control vs. 1.37±0.16 with NGF, P<0.05). Our findings suggest that the levels of P2X3 in primary afferent neurons are increased as the blood supply to the hindlimb is insufficient, and NGF is likely responsible for enhanced P2X3. (Supported by NIH R01 HL-090720, P01HL-096570, and AHA grant 0840130N).