title: Cation dependencies and turnover rates of the human K⁺-dependent Na⁺-Ca²⁺ exchangers NCKX1, NCKX2, NCKX3 and NCKX4.
abstract: The Solute Carrier Family 24 (SLC24) belongs to the CaCA super family of Ca(2+)/cation antiporters and codes for five different K(+)- dependent Na(+)- Ca(2+) exchangers (NCKX1-5). NCKX proteins play a critical role in Ca(2+) homeostasis in a wide variety of biological processes such as vision, olfaction, enamel formation, Melanocortin-4-receptor-dependent satiety and skin pigmentation. NCKX transcripts are widely found throughout the brain. In this study we examine the differences between NCKX1-4 in terms of cation dependencies. We measured changes to Ca(2+) influx via the reverse exchange mode while manipulating external Ca(2+) or K(+) or internal Na(+) concentrations (External Ca(2+) Dependence, External K(+) Dependence and Internal Na(+) Dependence respectively); we also looked at the effect of external Na(+)/Ca(2+) competition and 3' 4'-Dichlorobenzamil on the transport of ions in HEK 293 cell lines. A fluorescence based assay was used to determine differences in transport kinetics of the four membrane spanning exchangers using the Michaelis-Menten constant (Km). Our results show that there are no significant differences between the NCKX isoforms to explain the variation in the specific expression pattern of these exchangers.
authors.affiliation: Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Ali H
authors.initials: AH
authors.lastname: Jalloul
authors.affiliation: Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Szerencsei
authors.affiliation: Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada. Electronic address: pschnetk@ucalgary.ca.
authors.forename: Paul P M
authors.initials: PP
authors.lastname: Schnetkamp
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002412:Cations; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*
chemical_list: D017920:Antiporters; D002412:Cations; C430914:SLC24A3 protein, human; C470570:SLC24A4 protein, human; D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger; D012964:Sodium; D011188:Potassium; D002118:Calcium
keywords: Ca(2+) homeostasis; Fluorescence-based assay; Na(+)-Ca(2+) exchanger; Solute carrier family 24 (SLC24)