Essential role of Ca v 3.2 T-type calcium channels in butyrate-induced colonic pain and nociceptor hypersensitivity in mice

Given the role of Ca 3.2 isoform among T-type Ca channels (T-channels) in somatic and visceral nociceptive processing, we analyzed the contribution of Ca 3.2 to butyrate-induced colonic pain and nociceptor hypersensitivity in mice, to evaluate whether Ca 3.2 could serve as a target for treatment of visceral pain in irritable bowel syndrome (IBS) patients. Mice of ddY strain, and wild-type and Ca 3.2-knockout mice of a C57BL/6J background received intracolonic administration of butyrate twice a day for 3 days. Referred hyperalgesia in the lower abdomen was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load or chemicals was evaluated by counting nociceptive behaviors. Spinal phosphorylated ERK was detected by immunohistochemistry. Ca 3.2 knockdown was accomplished by intrathecal injection of antisense oligodeoxynucleotides. Butyrate treatment caused referred hyperalgesia and colonic hypersensitivity to distension in ddY mice, which was abolished by T-channel blockers and/or Ca 3.2 knockdown. Butyrate also increased the number of spinal phosphorylated ERK-positive neurons following colonic distension in the anesthetized ddY mice. The butyrate-treated ddY mice also exhibited T-channel-dependent colonic hypersensitivity to intracolonic Na S, known to enhance Ca 3.2 activity, and TRPV1, TRPA1 or proteinase-activated receptor 2 (PAR2) agonists. Wild-type, but not Ca 3.2-knockout, mice of a C57BL/6J background, after treated with butyrate, mimicked the T-channel-dependent referred hyperalgesia and colonic hypersensitivity in butyrate-treated ddY mice. Our study provides definitive evidence for an essential role of Ca 3.2 in the butyrate-induced colonic pain and nociceptor hypersensitivity, which might serve as a target for treatment of visceral pain in IBS patients.