Plasma membrane expression of T-type calcium channel α1 subunits is modulated by high voltage-activated auxiliary subunits

Abstract

It has been suggested that the auxiliary subunits of high voltage-activated (HVA) calcium channels modulate T-type, low voltage-activated (LVA) calcium channels. Such a regulation has yet to be documented, especially because there has been no biochemical characterization of T-channels. To monitor total protein levels and plasma membrane expression of T-channels in living cells, external epitopes (hemagglutinin, FLAG) were introduced into human recombinant Ca V3 channels that were also N-terminally fused to green fluorescent protein. Utilizing Western blot techniques, fluorescence flow cytometry, immunofluorescence, luminometry, and electrophysiology, we describe here that β1b and α2-δ1 subunits enhance the level of CaV3 proteins as well as their plasma membrane expression in various expression systems. We also report that, in both Xenopus oocytes and mammalian cells, the α2-δ1 and β1b subunits increase by at least 2-fold the current density of CaV3 channels with no change in the electrophysiological properties. Altogether, these data indicate that HVA auxiliary subunits modulate Ca V3 channel surface expression, suggesting that the membrane targeting of HVA and LVA α1 subunits is regulated dynamically through the expression of a common set of regulatory subunits.