|solute carrier family 24 (sodium/potassium/calcium exchanger), member 2
| Prinsen CF, Szerencsei RT, Schnetkamp PP. Molecular cloning and functional expression of the potassium-dependentsodium-calcium exchanger from human and chicken retinal cone photoreceptors.J Neurosci. 2000 Feb 15;20(4):1424-34. PMID: 10662833 [PubMed - indexed for MEDLINE]
Light causes a rapid lowering of cytosolic free calcium in the outer segments of both retinal rod and cone photoreceptors. This light-induced lowering of calcium is caused by extrusion via a Na-Ca exchanger located in the rod and cone outer segment plasma membrane and plays a key role in the process of light adaptation. The Na-Ca exchanger in retinal rod outer segment was shown earlier to be a novel Na-Ca+K exchanger (NCKX), and its cDNA was obtained by molecular cloning from several mammalian species. On the other hand, the proper identity of the retinal cone Na-Ca exchanger, in terms of both functional characteristics (e.g., requirement for and transport of potassium) and molecular identity, has not yet been elucidated. Here, we report the molecular cloning, intraretinal localization by in situ hybridization, and initial functional characterization of the chicken and human cone-specific Na-Ca exchangers. In addition we report the chicken rod-specific NCKX. We identified NCKX transcripts in both human and chicken cones and observed strong potassium-dependent Na-Ca exchange activity after heterologous expression of human and chicken cone NCKX cDNAs in cultured insect cells. In situ hybridization in chicken retina showed abundant rod NCKX transcripts only in rod photoreceptors, whereas abundant cone NCKX transcripts were found in most, if not all, cone photoreceptors and also in a subpopulation of retinal ganglion cells. A detailed comparison with the previously described retinal rod and brain NCKX cDNAs is presented.
>sp|Q9UI40|NCKX2_HUMAN Sodium/potassium/calcium exchanger 2 OS=Homo sapiens GN=SLC24A2 PE=1 SV=1 MDLQQSTTITSLEKWCLDESLSGCRRHYSVKKKLKLIRVLGLFMGLVAISTVSFSISAFSETDTQSTGEASVVSGPRVAQ GYHQRTLLDLNDKILDYTPQPPLSKEGESENSTDHAQGDYPKDIFSLEERRKGAIILHVIGMIYMFIALAIVCDEFFVPS LTVITEKLGISDDVAGATFMAAGGSAPELFTSLIGVFIAHSNVGIGTIVGSAVFNILFVIGMCALFSREILNLTWWPLFR DVSFYIVDLIMLIIFFLDNVIMWWESLLLLTAYFCYVVFMKFNVQVEKWVKQMINRNKVVKVTAPEAQAKPSAARDKDEP TLPAKPRLQRGGSSASLHNSLMRNSIFQLMIHTLDPLAEELGSYGKLKYYDTMTEEGRFREKASILHKIAKKKCHVDENE RQNGAANHVEKIELPNSTSTDVEMTPSSDASEPVQNGNLSHNIEGAEAQTADEEEDQPLSLAWPSETRKQVTFLIVFPIV FPLWITLPDVRKPSSRKFFPITFFGSITWIAVFSYLMVWWAHQVGETIGISEEIMGLTILAAGTSIPDLITSVIVARKGL GDMAVSSSVGSNIFDITVGLPLPWLLYTVIHRFQPVAVSSNGLFCAIVLLFIMLLFVILSIALCKWRMNKILGFIMFGLY FVFLVVSVLLEDRILTCPVSI