Involvement of Na
1.8 in acid-induced chronic muscle pain. (A, B) Dual acid injections spaced 2 (A) or 5 (B) days apart induced short-term hyperalgesia (2–4 days) in Na
1.8−/− mice. (C, D) Analgesic effect of NaV1.8-selective blocker A-803467 was tested at 3 days after mice have developed chronic hyperalgesia induced by dual intramuscular acid injection spaced 5 days apart. The A-803467 (70 mg/kg, i.p.) or vehicle was injected immediately after the baseline response (control) had been obtained. B, baseline on day 0; D, day. Blue and red arrows indicate the time mice receive intraperitoneal injection of vehicle or A-803467 respectively. *P < 0.05 compared with the response before the second acid injection or control.