Localization of the alpha(1F) Calcium channel subunit in the rat retina

PURPOSE. The molecular identity of the calcium channels that mediate glutam ate release from photoreceptors is unknown. Mutations in the recently ident ified, retina-specific alpha (1F) calcium channel subunit cause incomplete X-linked congenital stationary night blindness (CSNB2), the phenotype of wh ich is consistent with a defect in neurotransmission within the retina. The purpose of this study was to determine the cellular distribution of the an , subunit in the retina. METHODS. Antibodies were raised against a unique peptide from the human alp ha (1F) sequence. Rat retina sections were labeled with affinity-purified a lpha (1F) antibodies and the immunofluorescence analyzed by confocal micros copy. The alpha (1F) staining Was compared with that obtained with a pari-a l antibody, used to reveal the distribution of known voltage-gated calcium channels in the retina. Some sections were double labeled for alpha (1F) an d the photoreceptor synaptic ribbon marker, bassoon. RESULTS. Staining of retina sections with anti-alpha (1F) resulted in stron g punctate labeling in the outer plexiform layer (OPL) and weak punctate la beling in the inner plexiform layer (IPL), consistent with a synaptic local ization. Staining was also observed in the outer nuclear layer. Within the OPL, alpha (1F) immunoreactivity was clustered in discrete, horseshoe-shape d patches, the shape and dimensions of which are characteristic of rod acti ve zones. Similar structures were labeled with the pan-alpha (1) antibody. Localization of alpha (1F) immunoreactivity to rod active zones was confirm ed by double labeling for bassoon, a component of photoreceptor synaptic ri bbons. CONCLUSIONS. The distribution of alpha (1F) immunoreactivity in the OPL sug gests that calcium influx through alpha (1F) or alpha (1F)-like channels me diates glutamate release from rod photoreceptors.