Contribution of ASIC3 and TRPV1 to hyperalgesic priming in muscle nociceptors. (A,B) Dual intramuscular acid injections induced chronic hyperalgesia in Asic3+/+ mice but did not induce hyperalgesia in Asic3−/− mice. (C) Co-injection of acid with APETx2 (20 pmole) abolished the acid-induced transient hyperalgesia and prevented the development of long-lasting hyperalgesia with the second acid injection on day 5 in wild-type mice. (D) APETx2 (20 pmole) at the second acid injection produced only transient hyperalgesia in wild-type mice. (E-I) Mice received dual acid injections 1 day apart. The hyperalgesia lasted more than 12 days (E). Mice developed shorter terms of hyperalgesia up to 7 or 3 days with the first acid injection combined with 20 pmole (F) or 200 pmole (G) APETx2, respectively. (H) Co-injection of 20 pmole APETx2 and 1 nmole capsazepine in the first acid injection abolished the development of long-lasting hyperalgesia with the second acid injection. (I) Co-injection of acid and 1 nmole capsazepine shortened the second acid-induced hyperalgesia to 9 days. (J-L) Mice received dual acid injections 2 days apart. No coinjection (J), co-injection of acid and 20 pmole APETx2 (K), and co-injection of acid and 1 nmole capsazepine (L) had different effects on hyperalgesia duration induced by the second acid injection. Black arrows indicate when mice received intramuscular acid injections. Green, red, and purple arrows indicate when mice received the co-injection of acid with APETx2, capsazepine, and APETx2 combined with capsazepine respectively. B, baseline on day 0; D, day. *P < 0.05 compared with the response before the second acid injection.