CaV1.3 channels regulate excitability in many neurons. As is the case for all voltage-gated channels, it is widely assumed that individual CaV1.3 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 (CaV1.3S), but not the long (CaV1.3L), associates in functional clusters of two or more channels that open cooperatively, facilitating Ca(2+) influx. CaV1.3S channels are coupled via a C-terminus-to-C-terminus interaction that requires binding of the incoming Ca(2+) to calmodulin (CaM) and subsequent binding of CaM to the pre-IQ domain of the channels. Physically-coupled channels facilitate Ca(2+) currents as a consequence of their higher open probabilities, leading to increased firing rates in rat hippocampal neurons. We propose that cooperative gating of CaV1.3S channels represents a mechanism for the regulation of Ca(2+) signaling and electrical activity.

In the heart, reliable activation of Ca(2+) release from the sarcoplasmic reticulum during the plateau of the ventricular action potential requires synchronous opening of multiple CaV1.2 channels. Yet the mechanisms that coordinate this simultaneous opening during every heartbeat are unclear. Here, we demonstrate that CaV1.2 channels form clusters that undergo dynamic, reciprocal, allosteric interactions. This 'functional coupling' facilitates Ca(2+) influx by increasing activation of adjoined channels and occurs through C-terminal-to-C-terminal interactions. These interactions are initiated by binding of incoming Ca(2+) to calmodulin (CaM) and proceed through Ca(2+)/CaM binding to the CaV1.2 pre-IQ domain. Coupling fades as [Ca(2+)]i decreases, but persists longer than the current that evoked it, providing evidence for 'molecular memory'. Our findings suggest a model for CaV1.2 channel gating and Ca(2+)-influx amplification that unifies diverse observations about Ca(2+) signaling in the heart, and challenges the long-held view that voltage-gated channels open and close independently.