Characterization of Cav1.4 Complexes ({alpha}11.4, {beta}2, {alpha}2{delta}4) in HEK293T cells and in the Retina. [Neurobiology]

December 2nd, 2014 by Lee, A., Wang, S., Williams, B., Hagen, J., Scheetz, T. E., Haeseleer, F.

In photoreceptor synaptic terminals, voltage-gated Cav1.4 channels mediate Ca2+ signals required for transmission of visual stimuli. Like other high-voltage-activated Cav channels, Cav1.4 channels are comprised of a main pore-forming Cav1.4 α1 subunit, and auxiliary β and α2δ subunits. Of the four distinct classes of β and α2δ, β2 and α2δ4 are thought to co-assemble with Cav1.4 α1 subunits in photoreceptors. However, an understanding of the functional properties of this combination of Cav subunits is lacking. Here, we provide evidence that Cav1.4 α1, β2, and α2δ4 contribute to Cav1.4 channel complexes in the retina, and describe their properties in electrophysiological recordings. In addition, we identified a variant of β2, named here β2X13, which along with β2a, is present in photoreceptor terminals. Cav1.4 α1, β2, and α2δ4 were coimmunoprecipitated from lysates of transfected HEK293 cells and mouse retina, and were found to interact in the outer plexiform layer of the retina containing the photoreceptor synaptic terminals, by proximity ligation assays. In whole-cell patch clamp recordings of transfected HEK293T cells, channels (Cav1.4 α1 + β2X13) containing α2δ4 exhibited weaker voltage-dependent activation than those with α2δ1. Moreover, compared to channels (Cav1.4 α1 + α2δ4) with β2a, β2X13-containing channels exhibited greater voltage-dependent inactivation. The latter effect was specific to Cav1.4 as it was not seen for Cav1.2 channels. Our results provide the first detailed functional analysis of the Cav1.4 subunits that form native photoreceptor Cav1.4 channels, and indicate potential heterogeneity in these channels conferred by β2a and β2X13 variants.