DIFFERENTIAL-EFFECTS OF CA2-FORMATION WITH ALPHA(1S) AND ON CURRENT EXPRESSION IN TSA201 CELLS( CHANNEL BETA(1A) AND BETA(2A) SUBUNITS ON COMPLEX)

To study the interactions of the alpha(1S) subunit of the skeletal mus cle L-type Ca2+ channel with the skeletal beta(1a) and the cardiac bet a(2a), these subunits were expressed alone or in combination in tsA201 cells, Immunofluo rescence- and green fluorescent protein-labeling sh owed that, when expressed alone, beta(1a) was diffusely distributed th roughout the cytoplasm, beta(2a) was localized in the plasma membrane, and alpha(1S) was concentrated in a tubular/reticular membrane system , presumably the endoplasmic reticulum (ER), Upon coexpression with al pha(1S), beta(1a) became colocalized with alpha(1S) in the ER, Upon co expression with beta(2a), alpha(1S) redistributed to the plasma membra ne, where it aggregated in large clusters, Coexpression of alpha(1S) w ith beta(1a) but not with beta(2a) increased the frequency at which ce lls expressed L-type currents, A point mutation (alpha(1S)-Y366S) or d eletion (alpha(1S)-Delta 351-380) in the beta interaction domain of al pha(1S) blocked both translocation of beta(1a) to the ER and beta(2a)- induced translocation of the alpha(1S) mutants to the plasma membrane, However, the point mutation did not interfere with beta(1a)-induced c urrent stimulation, Thus, beta(1a) and beta(2a) are differentially dis tributed in tsA201 cells and upon coexpression with alpha(1S), form al pha(1S).beta complexes in different cellular compartments, Complex for mation but not current stimulation requires the intact beta interactio n domain in the I-II cytoplasmic loop of alpha(1S).