Role of the C terminus of the α(1c) (Ca(v)1.2) subunit in membrane targeting of cardiac L-type calcium channels

We have previously demonstrated that formation of a complex between L-type calcium (Ca²⁺) channel α(1C) (Ca(v)1.2) and β subunits was necessary to target the channels to the plasma membrane when expressed in tsA201 cells. In the present study, we identified a region in the C terminus of the α(1C) subunit that was required for membrane targeting. Using a series of C-terminal deletion mutants of the α(1C) subunit, a domain consisting of amino acid residues 1623-1666 ('targeting domain') in the C terminus of the α(1C) subunit has been identified to be important for correct targeting of L-type Ca²⁺ channel complexes to the plasma membrane. Although cells expressing the wild-type α(1C) and β(2a) subunits exhibited punctate clusters of channel complexes along the plasma membrane with little intracellular staining, co-expression of deletion mutants of the α(1C) subunit that lack the targeting domain with the β(2a) subunit resuited in an intracellular localization of the channels. In addition, three other regions in the C terminus of the α(1C) subunit that were downstream of residues 1623-1666 were found to contribute to membrane targeting of the L-type channels. Deletion of these domains in the α(1C) subunit resulted in a reduction of plasma membrane-localized channels, and a concomitant increase in channels localized intracellularly. Taken together, these results have demonstrated that a targeting domain in the C terminus of the α(1C) subunit was required for proper plasma membrane localization of the L-type Ca²⁺ channels.