title: The retinal rod and cone Na+/Ca2+-K+ exchangers.
abstract: The past few years has seen significant progress in our understanding of the retinal rod and cone Na+/Ca2+-K+ exchanger (NCKX) genes. The human rod and cone NCKX genes were localized to chromosomes 15q22 and 9p22, respectively. In situ hybridization localized the rod and cone NCKX transcripts in both human and chicken retinas: rod NCKX transcripts were found only in the inner segments of rods, whereas cone NCKX transcripts were found in a subset of retinal ganglion cells as well as in the inner segments of cones. We identified two sets of putative transmembrane spanning segments (TM's) as the only sequence elements strongly conserved between the rod and cone NCKX cDNAs, as well as between mammalian NCKX cDNAs and NCKX cDNAs cloned from lower organisms (C. elegans and Drosophila). The two sets of TM's make up less than onethird of the rod NCKX sequence and less than half of the cone NCKX sequence. Basic cation binding properties as inferred from an analysis of 45Ca transport rates and NCKX currents were very similar for all our NCKX clones, implying that conserved residues within the two sets of TM's contain all the residues involved in cation binding and cation transport.
authors.affiliation: Departments of Biophysics & Physiology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Clemens F M
authors.initials: CF
authors.lastname: Prinsen
authors.forename: Conan B
authors.initials: CB
authors.lastname: Cooper
authors.forename: Robert T
authors.initials: RT
authors.lastname: Szerencsei
authors.forename: Sabita K
authors.initials: SK
authors.lastname: Murthy
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Demetrick
authors.forename: Paul P M
authors.initials: PP
authors.lastname: Schnetkamp
mesh_terms: D000818:Animals; D002412:Cations; D002874:Chromosome Mapping; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007477:Ions; D008957:Models, Genetic; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D013997:Time Factors
chemical_list: D002412:Cations; D007477:Ions; D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger