Complexes of the α1C and β subunits generate the necessary signal for membrane targeting of class C L-type calcium channels

In the present study, we investigated the role of channel subunits in the membrane targeting of voltage-dependent L-type calcium channel complexes. We co-expressed the calcium channel pore-forming alpha(1C) Subunit with different accessory beta subunits in HEK-tsA201 cells and examined the subcellular localization of the channel subunits by immunohistochemistry using confocal microscopy and whole-cell radioligand binding studies. While the pore-forming alpha(1C) subunit exhibited perinuclear staining when expressed alone, and several of the wild-type and mutant beta subunits also exhibited intracellular staining, co-expression of the alpha(1C) subunit with either the wild-type beta(2a) subunit, a palmitoylation-deficient beta(2a)(C3S/C4S) mutant or three other nonpalmitoylated beta isoforms (beta(1b), beta(3), and beta(4) subunits) resulted in the redistribution of both the alpha(1C) and beta subunits into clusters along the cell surface. Furthermore, the redistribution of calcium channel complexes to the plasma membrane was observed when alpha(1C) was co-expressed with an N- and C-terminal truncated mutant beta(2a) containing only the central conserved regions. However, when the alpha(1C) subunit was co-expressed with an alpha(1)beta interaction-deficient mutant, beta(2a)BID(-), we did not observe formation of the channels at the plasma membrane. In addition, an Src homology 3 motif mutant of beta(2a) that was unable to interact with the alpha(1C) subunit also failed to target channel complexes to the plasma membrane. Interestingly, co-expression of the pore-forming alpha(1C) subunit with the largely peripheral accessory alpha(2)delta subunit was ineffective in recruiting alpha(1C) to the plasma membrane, while codistribution of all three subunits was observed when beta(2a) was co-expressed with the alpha(1C) and alpha(2)delta subunits, Taken together, our results suggested that the signal necessary for correct plasma membrane targeting of the class C L-type calcium channel complexes is generated as a result of a functional interaction between the alpha(1) and beta subunits.