Ca(V)1.2 channelopathic mutations evoke diverse pathophysiological mechanisms

The first pathogenic mutation in Ca(V)1.2 was identified in 2004 and was shown to cause a severe multisystem disorder known as Timothy syndrome (TS). The mutation was localized to the distal S6 region of the channel, a region known to play a major role in channel activation. TS patients suffer from life-threatening cardiac symptoms as well as significant neurodevelopmental deficits, including autism spectrum disorder (ASD). Since this discovery, the number and variety of mutations identified in Ca(V)1.2 have grown tremendously, and the distal S6 regions remain a frequent locus for many of these mutations. While the majority of patients harboring these mutations exhibit cardiac symptoms that can be well explained by known pathogenic mechanisms, the same cannot be said for the ASD or neurodevelopmental phenotypes seen in some patients, indicating a gap in our understanding of the pathogenesis of Ca(V)1.2 channelopathies. Here, we use whole-cell patch clamp, quantitative Ca(2+) imaging, and single channel recordings to expand the known mechanisms underlying the pathogenesis of Ca(V)1.2 channelopathies. Specifically, we find that mutations within the S6 region can exert independent and separable effects on activation, voltage-dependent inactivation (VDI), and Ca(2+)-dependent inactivation (CDI). Moreover, the mechanisms underlying the CDI effects of these mutations are varied and include altered channel opening and possible disruption of CDI transduction. Overall, these results provide a structure–function framework to conceptualize the role of S6 mutations in pathophysiology and offer insight into the biophysical defects associated with distinct clinical manifestations.