Carbon monoxide inhibition of Cav3.2 T-type Ca2+ channels reveals tonic modulation by thioredoxin

Boycott, H. E., Dallas, M. ORCID: https://orcid.org/0000-0002-5190-0522, Elies, J., Pettinger, L., Boyle, J. P., Scragg, J. L., Gamper, N. and Peers, C. (2013) Carbon monoxide inhibition of Cav3.2 T-type Ca2+ channels reveals tonic modulation by thioredoxin. FASEB Journal, 27 (8). pp. 3395-3407. ISSN 0892-6638 doi: 10.1096/fj.13-227249

Abstract/Summary

T-type Ca2+ channels play diverse roles in tissues such as sensory neurons, vascular smooth muscle, and cancers, where increased expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1) is often found. Here, we report regulation of T-type Ca2+ channels by carbon monoxide (CO) a HO-1 by-product. CO (applied as CORM-2) caused a concentration-dependent, poorly reversible inhibition of all T-type channel isoforms (Cav3.1-3.3, IC50 ∼3 μM) expressed in HEK293 cells, and native T-type channels in NG108-15 cells and primary rat sensory neurons. No recognized CO-sensitive signaling pathway could account for the CO inhibition of Cav3.2. Instead, CO sensitivity was mediated by an extracellular redox-sensitive site, which was also highly sensitive to thioredoxin (Trx). Trx depletion (using auranofin, 2-5 μM) reduced Cav3.2 currents and their CO sensitivity by >50% but increased sensitivity to dithiothreitol ∼3-fold. By contrast, Cav3.1 and Cav3.3 channels, and their sensitivity to CO, were unaffected in identical experiments. Our data propose a novel signaling pathway in which Trx acts as a tonic, endogenous regulator of Cav3.2 channels, while HO-1-derived CO disrupts this regulation, causing channel inhibition. CO modulation of T-type channels has widespread implications for diverse physiological and pathophysiological mechanisms, such as excitability, contractility, and proliferation