Localization of the inositol 1,4,5-trisphosphate receptor in synaptic terminals in the vertebrate retina

Inositol 1,4,5-trisphosphate (InsP₃) mobilizes internal Ca²⁺ in cells by binding to a receptor protein, which has recently been purified and molecularly cloned. To clarify those neuronal functions that are regulated by InsP₃, we have localized this (InsP₃) receptor protein immunocytochemically in the retina, a neural tissue of well-defined structure and function. Positive staining in neurons is confined almost exclusively to the synaptic layers. Using dissociated retinal neurons, we have further localized the receptor to presynaptic terminals of photoreceptors and bipolar cells, as well as the synaptic processes of amacrine cells. The specific association of InsP₃ receptors with synaptic terminals suggests a role for InsP₃ in synaptic modulation, especially with respect to transmitter release.