Autism-associated mutations in the CaVβ2 calcium-channel subunit increase Ba2+-currents and lead to differential modulation by the RGK-protein Gem

Voltage-gated calcium-channels (VGCCs) are heteromers consisting of several subunits. Mutations in the genes coding for VGCC subunits have been reported to be associated with autism spectrum disorder (ASD). In a previous study, we identified electrophysiologically relevant missense mutations of Caβ subunits of VGCCs. From this, we derived the hypothesis that several Caβ-mutations associated with ASD show common features sensitizing LTCCs and/or enhancing currents. Using a Caβ backbone, we performed extensive whole-cell and single-channel patch-clamp analyses of Ba currents carried by Ca1.2 pore subunits co-transfected with the previously described Caβ mutations (G167S, S197F) as well as a recently identified point mutation (V2D). Furthermore, the interaction of the mutated Caβ subunits with the RGK protein Gem was analyzed by co-immunoprecipitation assays and electrophysiological studies. Patch-clamp analyses revealed that all mutations increase Ba currents, e.g. by decreasing inactivation or increasing fraction of active sweeps. All Caβ mutations interact with Gem, but differ in the extent and characteristics of modulation by this RGK protein (e.g. decrease of fraction of active sweeps: Caβ > Caβ > Caβ). In conclusion, patch-clamp recordings of ASD-associated Caβ mutations revealed differential modulation of Ba currents carried by Ca1.2 suggesting kind of an "electrophysiological fingerprint" each. The increase in current finally observed with all Caβ mutations analyzed might contribute to the complex pathophysiology of ASD and by this indicate a possible underlying molecular mechanism.