Effect of Ca(v)β Subunits on Structural Organization of Ca(v)1.2 Calcium Channels

BACKGROUND: Voltage-gated Ca(v)1.2 calcium channels play a crucial role in Ca(2+) signaling. The pore-forming α(1C) subunit is regulated by accessory Ca(v)β subunits, cytoplasmic proteins of various size encoded by four different genes (Ca(v)β(1) - β(4)) and expressed in a tissue-specific manner. METHODS AND RESULTS: Here we investigated the effect of three major Ca(v)β types, β(1b), β(2d) and β(3), on the structure of Ca(v)1.2 in the plasma membrane of live cells. Total internal reflection fluorescence microscopy showed that the tendency of Ca(v)1.2 to form clusters depends on the type of the Ca(v)β subunit present. The highest density of Ca(v)1.2 clusters in the plasma membrane and the smallest cluster size were observed with neuronal/cardiac β(1b) present. Ca(v)1.2 channels containing β(3), the predominant Ca(v)β subunit of vascular smooth muscle cells, were organized in a significantly smaller number of larger clusters. The inter- and intramolecular distances between α(1C) and Ca(v)β in the plasma membrane of live cells were measured by three-color FRET microscopy. The results confirm that the proximity of Ca(v)1.2 channels in the plasma membrane depends on the Ca(v)β type. The presence of different Ca(v)β subunits does not result in significant differences in the intramolecular distance between the termini of α(1C), but significantly affects the distance between the termini of neighbor α(1C) subunits, which varies from 67 Å with β(1b) to 79 Å with β(3). CONCLUSIONS: Thus, our results show that the structural organization of Ca(v)1.2 channels in the plasma membrane depends on the type of Ca(v)β subunits present.