Background and aims: Cav3.2 T-type calcium channels, expressed in the primary afferents, play a pronociceptive role, and their function is regulated by a variety of extracellular substances; e.g. Zn2+ reduces Cav3.2 activity by binding to His191 in Cav3.2, an effect cancelled by L-cysteine and H2S, a gasotransmitter. Interestingly, ascorbic acid (vitamin C) suppresses Cav3.2 activity through metal-catalyzed oxidation of the Zn2+-binding His191. The present study thus examined the role of ascorbic acid in nociceptive processing, using the mice lacking gluconolactonase (GNL)/SMP30, an enzyme essential for ascorbic acid biosynthesis. Methods: T-type calcium channel-dependent currents (T-currents) were determined in NG108-15 cells that abundantly express Cav3.2. GNL/SMP30-KO and wild-type mice were subjected to dietary ascorbic acid restriction. Ascorbic acid levels were measured by HPLC. Somatic allodynia and referred hyperalgesia were assessed by von Frey test. Results: NaHS, an H2S donor, enhanced T-currents in NG108-15 cells, an effect abolished by ascorbic acid. The somatic allodynia and referred hyperalgesia following intraplantar and intracolonic NaHS, respectively, and paclitaxel-induced neuropathic allodynia in wild-type mice were suppressed by ascorbic acid or T-type calcium channel blockers. Dietary ascorbic acid restriction caused systemic ascorbic acid deficiency in GNL/SMP30-KO, but not wild-type, mice. The ascorbic acid restriction enhanced the NaHS-induced somatic and visceral hypersensitivity and paclitaxel-induced neuropathy in GNL/SMP30-KO mice, while it had no such effect in wild-type mice. Conclusions: Our data unveil the critical role of ascorbic acid in regulating Cav3.2-dependent somatic and visceral pain hypersensitivity.

DIETARY ASCORBIC ACID RESTRICTION IN GNL/SMP30-KNOCKOUT MICE UNVEILS THE ROLE OF ASCORBIC ACID IN REGULATION OF CAV3.2-DEPENDENT PAIN