Apparent lack of physical or functional interaction between Ca(V)1.1 and its distal C terminus

Ca(V)1.1 acts as both the voltage sensor that triggers excitation–contraction coupling in skeletal muscle and as an L-type Ca(2+) channel. It has been proposed that, after its posttranslational cleavage, the distal C terminus of Ca(V)1.1 remains noncovalently associated with proximal Ca(V)1.1, and that tethering of protein kinase A to the distal C terminus is required for depolarization-induced potentiation of L-type Ca(2+) current in skeletal muscle. Here, we report that association of the distal C terminus with proximal Ca(V)1.1 cannot be detected by either immunoprecipitation of mouse skeletal muscle or by colocalized fluorescence after expression in adult skeletal muscle fibers of a Ca(V)1.1 construct labeled with yellow fluorescent protein (YFP) and cyan fluorescent protein on the N and C termini, respectively. We found that L-type Ca(2+) channel activity was similar after expression of constructs that either did (YFP-Ca(V)1.1(1860)) or did not (YFP-Ca(V)1.1(1666)) contain coding sequence for the distal C-terminal domain in dysgenic myotubes null for endogenous Ca(V)1.1. Furthermore, in response to strong (up to 90 mV) or long-lasting prepulses (up to 200 ms), tail current amplitudes and decay times were equally increased in dysgenic myotubes expressing either YFP-Ca(V)1.1(1860) or YFP-Ca(V)1.1(1666), suggesting that the distal C-terminal domain was not required for depolarization-induced potentiation. Thus, our experiments do not support the existence of either biochemical or functional interactions between proximal Ca(V)1.1 and the distal C terminus.