Role of T-type Ca2+ channels in the heart

After the first demonstration 30 years ago that Ca2+ could permeate through two different channels, the occurrence and role of T-type Ca2+ current, I-CaT have been the matter of hundreds of publications, including the two 1985' reports in various cardiac tissues and species. Except for its specific biophysical characteristics, I-CaT is no longer so easily distinguished from the L-type Ca2+ current, I-CaL, since it is also sensitive to multiple compounds and various neuromediators including the beta-adrenergic agonists. Changes in I-CaT occur during development, so that while it is recorded in all embryonic and neonatal cells investigated, I-CaT has been reported in adult ventricular cells of only few species in control. However, under various pathological conditions, I-CaT is often recorded at some phases of remodelling at least in some localized area and one or more of the three channel proteins, Cav3.1-3.3 are clearly re-expressed under the influence of IGF-1, endothelin, and angiotensin II-I-CaT contributes to the control of electrical activity including pacemaker and arrhythmia. Furthermore I-CaT, and its low-depolarisation window current, participate in Ca2+ entry, so that I-CaT has been involved in the release of Ca2+ from internal stores, the Ca2+,induced Ca2+ release mechanism, although at much lower level than I-CaL. I-CaT contributes also to Ca2+-dependent hormonal secretion. This review further emphasizes the difficulties encountered in analysing this current. (c) 2006 Elsevier Ltd. All rights reserved.