Evidence for the participation of Ca²⁺-activated chloride channels in formalin-induced acute and chronic nociception

In this study we determined the role of Ca²⁺-activated chloride channels (CaCC) in acute and chronic nociceptive responses elicited by 1% formalin. Formalin injection produced a typical pattern of flinching behavior for about 1 h. Moreover, it produced secondary allodynia and hyperalgesia in the ipsilateral and contralateral paws for at least 6 days. Local peripheral and intrathecal pre-treatment (-10 min) with the non-selective and selective CaCC blockers niflumic acid and CaCC_inh-A01, respectively, prevented formalin-induced flinching behavior mainly during phase 2 of the formalin test. Furthermore, niflumic acid and CaCC_inh-A01 also prevented in a dose-dependent manner the long-lasting evoked secondary mechanical allodynia and hyperalgesia in the ipsilateral and contralateral paws. Moreover, local peripheral and intrathecal post-treatment (on day 6) with both CaCC blockers decreased the established formalin-induced secondary mechanical allodynia and hyperalgesia behavior in both paws. CaCC anoctamin-1 and bestrophin-1 were detected in the dorsal root ganglia. Formalin injection increased anoctamin-1, but not bestrophin-1 protein levels at 6 days. Intrathecal injection of the CaCC inhibitor CaCC_inh-A01 prevented formalin-induced anoctamin-1 increase. Data suggest that peripheral and spinal CaCC, and particularly anoctamin-1, participates in the acute nociception induced by formalin as well as in the development and maintenance of secondary mechanical allodynia and hyperalgesia. Thus, CaCC activity contributes to neuronal excitability in the process of nociception induced by formalin.