Ca2+ entry into neurons is facilitated by cooperative gating of clustered CaV1.3 channels

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 Ca2+ influx. CaV1.3S 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 CaV1.3S channels represents a mechanism for the regulation of Ca2+ signaling and electrical activity. The electrical charge inside a cell is different from that outside of the cell. Neurons rely on this difference to send signals via electrical impulses. This process involves ions moving across the neuron’s membrane through proteins called ion channels. Cav1.3 channels are ion channels that open when the membrane’s electrical charge changes to allow positively charged calcium ions into the cell. This generates an electrical current that enables neurons in the brain to produce repetitive impulses. Calcium ions entering through a Cav1.3 channel can encourage the channel to allow in even more calcium ions. A closely related channel called Cav1.2, which is essential to the activity of heart muscle, behaves in a similar way. Researchers have recently found that Cav1.2 channels are arranged in clusters in the membrane and that adjacent channels interact to allow more calcium ions through the channels. This was an unexpected finding because it had long been thought that all ion channels acted independently. Moreno et al. have now used a range of different approaches to investigate the behavior of one form of the Cav1.3 channel, called CaV1.3S, in human cells and in neurons from rat brains. Initial experiments confirmed that calcium ions stimulated these channels to open in a coordinated way and to allow in more calcium. High-resolution microscopy then revealed that the CaV1.3S channels do form cl