Peripheral acid-sensing ion channels and P2X receptors contribute to mechanical allodynia in a rodent thrombus-induced ischemic pain model

We have previously established a thrombus-induced ischemic pain (TIIP) model in the rat, which mimics the pathophysiology of ischemic pain in patients with peripheral arterial disease. Because ischemia commonly induces acidosis and ATP release, one of the goals of this study was to investigate the role of acid-sensing ion channels (ASICs), transient receptor potential vanilloid-1 (TRPV1) receptors, and P2X receptors in the maintenance of ischemia-induced mechanical allodynia (MA). To test this, amiloride (an ASIC blocker), AMG-9810 (a TRPV1 blocker), or PPADS (a P2Xs antagonist) was intraplantarly injected at day 3 after FeCl₂ application onto the femoral artery. Ipsilateral administration of amiloride or PPADS but not AMG-9810 dose-dependently reduced MA. However, contralateral amiloride or PPADS did not suppress contralateral MA. Interestingly, co-administration of submaximal doses of amiloride and PPADS produced a significantly prolonged suppression of MA. Furthermore, ipsilateral EGTA (a calcium chelator) or chelerythrine (a protein kinase C inhibitor) also significantly reduced MA. Collectively, these findings suggest that peripheral ASICs and P2X receptors are involved in the maintenance of TIIP, which is possibly mediated by a Ca²⁺-protein kinase C signaling mechanism. These results provide mechanistic information about peripheral ischemic nociception that may be useful for developing better therapeutic management of ischemic pain in patients with peripheral arterial disease. Perspective: The results of the current study demonstrate that peripheral administration of an ASICs blocker or P2X antagonist significantly suppress TIIP. Co-administration of submaximal doses of ASIC and P2X antagonists produced an even greater effect. These results implicate peripheral ASICs and P2X receptors in the maintenance of thrombus-induced ischemic pain.