Characterization of Cav1.4 complexes (?11.4, ?2, and ?2?4) in HEK293T cells and in the retina.

ABSTRACT: In photoreceptor synaptic terminals, voltage-gated Cav1.4 channels mediate Ca(2+) signals required for transmission of visual stimuli. Like other high voltage-activated Cav channels, Cav1.4 channels are composed of a main pore-forming Cav1.4 ?1 subunit and auxiliary ? and ?2? subunits. Of the four distinct classes of ? and ?2?, ?2 and ?2?4 are thought to co-assemble with Cav1.4 ?1 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 ?1, ?2, and ?2?4 contribute to Cav1.4 channel complexes in the retina and describe their properties in electrophysiological recordings. In addition, we identified a variant of ?2, named here ?2X13, which, along with ?2a, is present in photoreceptor terminals. Cav1.4 ?1, ?2, and ?2?4 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 ?1 + ?2X13) containing ?2?4 exhibited weaker voltage-dependent activation than those with ?2?1. Moreover, compared with channels (Cav1.4 ?1 + ?2?4) with ?2a, ?2X13-containing channels exhibited greater voltage-dependent inactivation. The latter effect was specific to Cav1.4 because 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 ?2a and ?2X13 variants.

SUBMITTER: Lee A 

PROVIDER: S-EPMC4340398 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature