Cloning and immunocytochemical localization of a cyclic nucleotide-gated channel alpha-subunit to all cone photoreceptors in the mouse retina

Cyclic nucleotide-gated channels (CNGC) are ligand-gated ion channels that open and close in response to changes in the intracellular concentration of the second messengers, 3',5'-cyclic adenosine monophosphate and 3',5'-cycl ic guanosine monophosphate. Most notably, they transduce the chemical signa l produced by the absorption of light in photoreceptors into a membrane pot ential change, which is then transmitted to the ascending visual pathway. C NGCs have also been implicated in the signal transduction of other neurons downstream of the photoreceptors, in particular the ON-bipolar cells, as we ll as in other areas of the central nervous system. We therefore undertook a search for additional cyclic nucleotide- gated channels expressed in the retina. Following a degenerate reverse transcription polymerase chain react ion approach to amplify low-copy number messages, a cDNA encoding a new spl ice variant of CNGC oc-subunit was isolated from mouse retina and classifie d as mCNG3. An antiserum raised against the carboxy-terminal sequence ident ified the retinal cell type expressing mCNG3 as cone photoreceptors. Preemb edding immunoelectron microscopy demonstrated its membrane localization in the outer segments, consistent with its role in phototransduction. Double-l abeling experiments with cone-specific markers indicated that all cone phot oreceptors in the murid retina use the same or a highly conserved cyclic nu cleotide-gated channel. Therefore, defects in this channel would be predict ed to severely impair photopic vision. J. Comp. Neurol. 421:80-94, 2000. (C ) 2000 Wiley-Liss, Inc.