Dominant-negative synthesis suppression of voltage-gated calcium channel Ca(v)2.2 induced by truncated constructs

Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV ), each with six transmembrane segments. A number of truncated isoforms hav e been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha 1B) of its coexpression with truncated constructs of Ca(v) 2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta 1b and alpha2 delta -1, did not form funct ional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functi onal expression, although at the single channel level, when channels were r ecorded, there were no differences in their biophysical properties. Further more, when it was coexpressed with either domain I-II or domain I, the fluo rescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v )2.2 protein was almost abolished. Suppression does not involve sequestrati on of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also o ccurred in the absence of beta subunit, and the effect of domain I-II or do main I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It r equires transmembrane segments, because the isolated Ca(v)2.2 N terminus di d not have any effect. Our results indicate that the mechanism of suppressi on of Ca(v)2.2 by truncated constructs containing domain I involves inhibit ion of channel synthesis, which may represent a role of endogenously expres sed truncated Ca-v isoforms.