title: Relationship between intracellular Na+ concentration and reduced Na+ affinity in Na+,K+-ATPase mutants causing neurological disease.
abstract: The neurological disorders familial hemiplegic migraine type 2 (FHM2), alternating hemiplegia of childhood (AHC), and rapid-onset dystonia parkinsonism (RDP) are caused by mutations of Na(+),K(+)-ATPase α2 and α3 isoforms, expressed in glial and neuronal cells, respectively. Although these disorders are distinct, they overlap in phenotypical presentation. Two Na(+),K(+)-ATPase mutations, extending the C terminus by either 28 residues ("+28" mutation) or an extra tyrosine ("+Y"), are associated with FHM2 and RDP, respectively. We describe here functional consequences of these and other neurological disease mutations as well as an extension of the C terminus only by a single alanine. The dependence of the mutational effects on the specific α isoform in which the mutation is introduced was furthermore studied. At the cellular level we have characterized the C-terminal extension mutants and other mutants, addressing the question to what extent they cause a change of the intracellular Na(+) and K(+) concentrations ([Na(+)]i and [K(+)]i) in COS cells. C-terminal extension mutants generally showed dramatically reduced Na(+) affinity without disturbance of K(+) binding, as did other RDP mutants. No phosphorylation from ATP was observed for the +28 mutation of α2 despite a high expression level. A significant rise of [Na(+)]i and reduction of [K(+)]i was detected in cells expressing mutants with reduced Na(+) affinity and did not require a concomitant reduction of the maximal catalytic turnover rate or expression level. Moreover, two mutations that increase Na(+) affinity were found to reduce [Na(+)]i. It is concluded that the Na(+) affinity of the Na(+),K(+)-ATPase is an important determinant of [Na(+)]i.
authors.affiliation: From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark and.
authors.forename: Mads S
authors.initials: MS
authors.lastname: Toustrup-Jensen
authors.forename: Anja P
authors.initials: AP
authors.lastname: Einholm
authors.forename: Vivien R
authors.initials: VR
authors.lastname: Schack
authors.forename: Hang N
authors.initials: HN
authors.lastname: Nielsen
authors.forename: Rikke
authors.initials: R
authors.lastname: Holm
authors.forename: María-Jesús
authors.initials: MJ
authors.lastname: Sobrido
authors.forename: Jens P
authors.initials: JP
authors.lastname: Andersen
authors.forename: Torben
authors.initials: T
authors.lastname: Clausen
authors.forename: Bente
authors.initials: B
authors.lastname: Vilsen
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D020821:Dystonic Disorders / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport / Q000235:genetics; D020325:Migraine with Aura / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D011188:Potassium / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: C488756:ATP1A3 protein, human; D012964:Sodium; C498531:ATP1A2 protein, human; C498532:Atp1a2 protein, rat; C541459:Atp1a3 protein, rat; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium
keywords: Enzyme Mutation; Familial Hemiplegic Migraine; Intracellular Sodium; Membrane Transport; Na,K-ATPase; Neurological Diseases; Rapid-onset Dystonia Parkinsonism; Sodium Transport