Complexes of the alpha(1C) and beta subunits generate the necessary signalfor membrane targeting of class C L-type calcium channels

In the present study, we investigated the role of channel subunits in the m embrane targeting of voltage-dependent L-type calcium channel complexes. We co-expressed the calcium channel pore-forming alpha(1C) Subunit with diffe rent accessory beta subunits in HEK-tsA201 cells and examined the subcellul ar localization of the channel subunits by immunohistochemistry using confo cal microscopy and whole-cell radioligand binding studies. While the pore-f orming alpha(1C) subunit exhibited perinuclear staining when expressed alon e, and several of the wild-type and mutant beta subunits also exhibited int racellular staining, co-expression of the alpha(1C) subunit with either the wild-type beta(2a) subunit, a palmitoylation-deficient beta(2a)(C3S/C4S) m utant 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 redis tribution 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 a lpha(1C) subunit was co-expressed with an alpha(1)beta interaction-deficien t mutant, beta(2a)BID(-), we did not observe formation of the channels at t he 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 targ et channel complexes to the plasma membrane. Interestingly, co-expression o f 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 bet a(2a) was co-expressed with the alpha(1C) and alpha(2)delta subunits, Taken together, our results suggested that the signal necessary for correct plas ma membrane targeting of the class C L-type calcium channel complexes is ge nerated as a result of a functional interaction between the alpha(1) and be ta subunits.