Ca2+ entry into neurons is facilitated by cooperative gating of clustered Cav1.3 channels

Ca(v)1.3 channels regulate excitability in many neurons. As is the case for all voltage gated channels, it is widely assumed that individual Ca(v)1.3 channels behave independently with respect to voltage-activation, open probability, and facilitation. Here, we report the results of super-resolution imaging, optogenetic, and electrophysiological measurements that refute this long-held view. We found that the short channel isoform (Ca(v)1.3(s)), but not the long (Ca(v)1.3(L)), associates in functional clusters of two or more channels that open cooperatively, facilitating Ca2+ influx. Ca(v)1.3(s) channels are coupled via a C-terminus-to-C-terminus interaction that requires binding of the incoming Ca2+ to calmodulin (CaM) and subsequent binding of CaM to the pre-IQ domain of the channels. Physically-coupled channels facilitate Ca2+ currents as a consequence of their higher open probabilities, leading to increased firing rates in rat hippocampal neurons. We propose that cooperative gating of Ca(v)1.3(s) channels represents a mechanism for the regulation of Ca2+ signaling and electrical activity.