Abstract
T-type calcium channels encoded by the Ca V 3.2 isoform are expressed in nociceptive primary afferent neurons where they contribute to hyperalgesia and thus are considered as a potential therapeutic target to treat pathological pain. Here we report that the small organic state-dependent T-type channel antagonist TTA-A2 efficiently inhibits recombinant and native Ca V 3.2 currents. Although TTA-A2 is a pan Ca V 3 blocker, it demonstrates a higher potency for Ca V 3.2 compared to Ca V 3.1. TTA-A2 selectivity for T-type currents was demonstrated in sensory neurons where it lowered cell excitability uniquely on neurons expressing T-type channels. In vivo pharmacology in Ca V 3.2 knockout and wild type mice reveal that TTA-A2-mediated antinociception critically depends on Ca V 3.2 expression. The pathophysiology of irritable bowel syndrome (IBS) was recently demonstrated to involve Ca V 3.2 in a rat model of this disease. Oral administration of TTA-A2 produced a dose-dependent reduction of hypersensitivity in an IBS model, demonstrating its therapeutic potential for the treatment of pathological pain. Overall, our results suggest that the high potency of TTA-A2 in the depolarized state strengthen its analgesic efficacy and selec-tivity toward pathological pain syndromes. This characteristic would be beneficial for the development of analgesics targeting T-type channels, in particular for the treatment of pain associated with IBS. Ó