Modulates calcium-dependent activity of inositol 1,4,5-triphosphate receptors (ITPRs). Inhibits agonist-induced intracellular calcium signaling (By similarity). Enhances inactivation and does not support calcium-dependent facilitation of voltage-dependent P/Q-type calcium channels (PubMed:11865310). Causes calcium-dependent facilitation and inhibits inactivation of L-type calcium channels by binding to the same sites as calmodulin in the C-terminal domain of CACNA1C, but has an opposite effect on channel function. Suppresses the calcium-dependent inactivation of CACNA1D. Inhibits TRPC5 channels. Prevents NMDA receptor-induced cellular degeneration. Required for the normal transfer of light signals through the retina (By similarity). Interacts ITPR1, ITPR2 and ITPR3. The strength of this interaction inversely correlates with calcium concentration. Interacts with CACNA1A (via C-terminal CDB motif) in the pre- and postsynaptic membranes. Interacts with CACNA1C. Interacts with CACNA1D (By similarity). Interacts (via EF-hands 1 and 2) at microtubules with MAP1LC3B. Interacts (via EF-hands 1 and 2) with NSMF (via the central NLS-containing motif region), the interaction occurs in a calcium dependent manner after synaptic NMDA receptor stimulation and prevents nuclear import of NSMF. Interacts with MYO1C and TRPC5. Interacts with SPACA9 (By similarity). Occurs in both the cytoplasmic and cytoskeletal compartment of cell somata and dendrites. Somatodendritic compartment of neurons (PubMed:11906216). Restricted expression in retina to a subpopulation of amacrine, bipolar, and ganglion cells (PubMed:11906216). According to PubMed:11906216, expression is heterogeneous within brain regions and their major cell types and does not match with those of marker proteins for characterized neuronal subpopulations (PubMed:11906216). Isoform 2: Minor isoform expressed in the brain, in the granule cell layer of the cerebellum, at low level. Not developmentally regulated (PubMed:11906216). Isoform 3: Minor isoform expressed in the brain, in the granule cell layer (PubMed:11906216). of the cerebellum, at low level. Not developmentally regulated. Its expression is regulated differentially in retinal cell types during development. EF-1 binds magnesium constitutively under physiological conditions, EF-3 and EF-4 bind calcium cooperatively and EF-2 binds neither calcium nor magnesium. Phosphorylated. The phosphorylation regulates the activity (By similarity). Major isoform expressed in the brain.