Expression of the α_1F calcium channel subunit by photoreceptors in the rat retina

Purpose: The CACNA1F gene encodes a voltage-gated calcium channel α₁ subunit, α_1F, which is expressed in the human retina. Mutations in this gene cause incomplete X-linked congenital stationary night blindness (CSNB2). The aim of this study was to obtain the sequence of the rat α_1F cDNA and localize the encoded polypeptide in the rat retina. Methods: The full-length rat α_1F sequence was compiled from sequencing of overlapping α_1F PCR fragments amplified from rat retinal cDNA. Antiserum was raised against a human α_1F peptide. It was found that the human α_1F peptide used to generate the antiserum was conserved at only 11 out of 19 residues in the cloned rat sequence. Therefore, antibodies were affinity purified against either the human α_1F peptide or the equivalent rat peptide and used for immunofluorescent staining of rat retina sections. Results: The rat α_1F amino acid sequence was found to be 91% and 95% identical to the human and mouse α_1F sequences, respectively. Antibodies affinity purified against the human α_1F peptide stained both the outer nuclear layer (ONL) and outer plexiform layer of rat retina sections. In contrast, staining with antibodies affinity purified against the corresponding rat α_1F peptide was restricted to the ONL. Conclusions: The rat α_1F amino acid sequence is highly homologous to the human and mouse sequences. The immunohistochemical results indicate the existence of distinct α_1F isoforms or α_1F-like channels, which are differentially distributed in the cell bodies and synaptic terminals of photoreceptors in the rat retina.