• alpha1I;
  • Cav3.3;
  • HEK-293;
  • low voltage activated;
  • NG 108-15;
  • splice variant;
  • T-type calcium channels;
  • Xenopus oocytes


The recently cloned T-type calcium channel α1I (Cav3.3) displays atypically slow kinetics when compared to native T-channels. Possible explanations might involve alternative splicing of the α1I subunit, or the use of expression systems that do not provide a suitable environment (auxiliary subunit, phosphorylation, glycosylation…). In this study, two human α1I splice variants, the α1I-a and α1I-b isoforms that harbour distinct carboxy-terminal regions were studied using various expression systems. As the localization of the α1I subunit is primarily restricted to neuronal tissues, its functional expression was conducted in the neuroblastoma/glioma cell line NG 108-15, and the results compared to those obtained in HEK-293 cells and Xenopus oocytes. In Xenopus oocytes, both isoforms exhibited very slow current kinetics compared to those obtained in HEK-293 cells, but the α1I-b isoform generated faster currents than the α1I-a isoform. Both activation and inactivation kinetics of α1I currents were significantly faster in NG 108-15 cells, while deactivating tail currents were two times slower, compared to those obtained in HEK-293 cells. Moreover, the α1I-b isoform showed significantly slower deactivation kinetics both in NG 1080-15 and in HEK-293 cells. Altogether, these data emphasize the advantage of combining several expression systems to reveal subtle differences in channel properties and further indicate that the major functional differences between both human α1I isoforms are related to current kinetics. More importantly, these data suggest that the expression of the α1I subunit in neuronal cells contributes to the ‘normalization’ of current kinetics to the more classical, fast-gated T-type Ca2+ current.