Localization of the α_1F calcium channel subunit in the rat retina

Purpose. The molecular identity of the calcium channels that mediate glutamate release from photoreceptors is unknown. Mutations in the recently identified, retina-specific α_1F calcium channel subunit cause incomplete X-linked congenital stationary night blindness (CSNB2), the phenotype of which is consistent with a defect in neurotransmission within the retina. The purpose of this study was to determine the cellular distribution of the α_1F subunit in the retina. Methods. Antibodies were raised against a unique peptide from the human a α_1F sequence. Rat retina sections were labeled with affinity-purified α_1F antibodies and the immunofluorescence analyzed by confocal microscopy. The α_1F staining was compared with that obtained with a pan-α₁ antibody, used to reveal the distribution of known voltage-gated calcium channels in the retina. Some sections were double labeled for α_1F and the photoreceptor synaptic ribbon marker, bassoon. Results. Staining of retina sections with anti-α_1F resulted in strong punctate labeling in the outer plexiform layer (OPL) and weak punctate labeling in the inner plexiform layer (IPL), consistent with a synaptic localization. Staining was also observed in the outer nuclear layer. Within the OPL, α_1F immunoreactivity was clustered in discrete, horseshoe-shaped patches, the shape and dimensions of which are characteristic of rod active zones. Similar structures were labeled with the pan-α₁ antibody. Localization of α_1F immunoreactivity to rod active zones was confirmed by double labeling for bassoon, a component of photoreceptor synaptic ribbons. Conclusions. The distribution of α_1F immunoreactivity in the OPL suggests that calcium influx through α_1F or α_1F-like channels mediates glutamate release from rod photoreceptors.