Calcium channels at ribbon synapses in the retina

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DESCRIPTION (provided by applicant): Recently the gene causing incomplete congenital stationary night blindness (CSNB2) was identified and found to encode a retina-specific, voltage-activated calcium channel, alpha-1F. The disease is characterized by severely reduced nighttime (or rod-mediated) vision as well as abnormalities in daytime (or cone-mediated) vision. The electrophysiological and psychophysical phenotype of CSNB2 can be explained by a defect in synaptic transmission within the retina. We have found that the alpha-1F calcium channel is localized to rod photoreceptor and rod bipolar cell synaptic terminals in the rat and mouse retinas consistent with the night-blindness associated with CSNB2. Voltage-activated calcium channels are essential to the first two stages of visual processing in the retina, which occur at photoreceptor and bipolar cell ribbon synapses. At the ribbon synapse, calcium channels couple the graded electrical responses of the photoreceptor or bipolar cell to calcium-dependent, graded release of the excitatory neurotransmitter, glutamate. Our data suggest that the symptoms of CSNB2 are caused by a block of glutamate release at photoreceptor and bipolar cell ribbon synapses. A detailed characterization of the alpha -1F calcium channel is essential to understanding both the complex phenotype of CSNB2 and normal synaptic transmission in the retina. Yet the biophysical properties of alpha-1F calcium channels are not known. Nor is it known whether alpha-1F is present in cone photoreceptor and cone bipolar cell terminals, or whether other calcium channels mediate glutamate release in the cone pathway. The proposed experiments will address these questions. The Specific Aims are to 1. Determine in detail the distribution and functional properties of the alpha-1F calcium channel subunit. 2. Identify retinal proteins that interact with alpha-1F. 3. Identify other voltage-activated calcium channels at retinal ribbon synapses. We will use a multidisciplinary approach involving molecular, biochemical, immunohistochemical and electrophysiological techniques to achieve these aims. The results of these experiments will provide insight into the composition and functional organization of retinal ribbon synapses and into the perturbation of retinal function associated with CSNB2.