Characterization of auto-regulation of the human cardiac α1 subunit of the L-type calcium channel: Importance of the C-terminus

The carboxyl terminal of the L-type calcium channel α1C subunit comprises approximately one third of the primary structure of the α1 subunit (> 700 amino acids residues). This region is sensitive to limited posttranslational processing. In heart and brain the α1C subunits are found to be truncated but the C-terminal domain remains functionally present. Based on our previous data we hypothesized that the distal C-terminus (approximately residues 1650–1950) harbors an important, predominantly inhibitory domain. We generated C-terminal-truncated α1C mutants, and after expressing them in combination with a β3 subunit in HEK-293 cells, electrophysiological experiments were carried out. In order to dissect the important inhibitory part of the C-terminus, trypsin was dialyzed into the cells. The data provide evidence that there are multiple residues within the inhibitory domain that are crucial to the inhibitory process as well as to the enhancement of expressed current by intracellular application of proteases. In addition, the expression of the chimeric mutant α1CΔ1673-DRK1 demonstrated that the C-terminal is specific for the heart channel.