A calcium channel that regulates synaptic endocytosis and hence couples exo- with endocytosis. Isoform A and isoform B are mainly required in the nervous system and necessary in photoreceptor cells. Homomultimer; Isoform B. Upon fusion of the synaptic vesicle with the presynaptic membrane, protein is present in the periactive zones, where endocytosis is known to occur. Isoform B is expressed in the neuropils of embryonic, larval, adult CNS, and R1-R6 terminals. Expression in the central nervous system (CNS) starts at embryonic stage 13. Impaired intracellular resting calcium levels and impaired endocytosis in presynaptic terminals, exocytosis is normal. Mutant boutons at the neuromuscular junctions exhibit a significant depletion in the number of synaptic vesicles. There are numerous extra boutons which are often small, clustered, and flowery in nature. Mutant nerve terminals display omega structures and collared pits. Belongs to the calcium channel flower family.