Expression of the alpha(1F) calcium channel subunit by photoreceptors in the rat retina

Purpose: The CACNA1F gene encodes a voltage-gated calcium channel alpha (1) subunit, alpha (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 alpha ( 1F) cDNA and localize the encoded polypeptide in the rat retina. Methods: The full-length rat alpha (1F) sequence was compiled from sequenci ng of overlapping alpha (1F) PCR fragments amplified from rat retinal cDNA. Antiserum was raised against a human alpha (1F) peptide. It was found that the human alpha (1F) peptide used to generate the antiserum was conserved at only 11 out of 19 residues in the cloned rat sequence. Therefore, antibo dies were affinity purified against either the human alpha (1F) peptide or the equivalent rat peptide and used for immunofluorescent staining of rat r etina sections. Results: The rat alpha (1F) amino acid sequence was found to be 91% and 95% identical to the human and mouse alpha (1F) sequences, respectively. Antib odies affinity purified against the human alpha (1F) peptide stained both t he outer nuclear layer (ONL) and outer plexiform layer of rat retina sectio ns. In contrast, staining with antibodies affinity purified against the cor responding rat alpha (1F) peptide was restricted to the ONL. Conclusions: The rat alpha (1F) amino acid sequence is highly homologous to the human and mouse sequences. The immunohistochemical results indicate th e existence of distinct alpha (1F) isoforms or alpha (1F)-like channels, wh ich are differentially distributed in the cell bodies and synaptic terminal s of photoreceptors in the rat retina.