A dual role for Ca1.4 Ca channels in the molecular and structural organization of the rod photoreceptor synapse.

Synapses are fundamental information processing units that rely on voltage-gated Ca (Ca) channels to trigger Ca-dependent neurotransmitter release. Ca channels also play Ca-independent roles in other biological contexts, but whether they do so in axon terminals is unknown. Here, we addressed this unknown with respect to the requirement for Ca1.4 L-type channels for the formation of rod photoreceptor synapses in the retina. Using a mouse strain expressing a non-conducting mutant form of Ca1.4, we report that the Ca1.4 protein, but not its Ca conductance, is required for the molecular assembly of rod synapses; however, Ca1.4 Ca signals are needed for the appropriate recruitment of postsynaptic partners. Our results support a model in which presynaptic Ca channels serve both as organizers of synaptic building blocks and as sources of Ca ions in building the first synapse of the visual pathway and perhaps more broadly in the nervous system.