title: Na+/K+-ATPase α-subunit (nkaα) isoforms and their mRNA expression levels, overall Nkaα protein abundance, and kinetic properties of Nka in the skeletal muscle and three electric organs of the electric eel, Electrophorus electricus.
abstract: This study aimed to obtain the coding cDNA sequences of Na+/K+-ATPase α (nkaα) isoforms from, and to quantify their mRNA expression in, the skeletal muscle (SM), the main electric organ (EO), the Hunter's EO and the Sach's EO of the electric eel, Electrophorus electricus. Four nkaα isoforms (nkaα1c1, nkaα1c2, nkaα2 and nkaα3) were obtained from the SM and the EOs of E. electricus. Based on mRNA expression levels, the major nkaα expressed in the SM and the three EOs of juvenile and adult E. electricus were nkaα1c1 and nkaα2, respectively. Molecular characterization of the deduced Nkaα1c1 and Nkaα2 sequences indicates that they probably have different affinities to Na+ and K+. Western blotting demonstrated that the protein abundance of Nkaα was barely detectable in the SM, but strongly detected in the main and Hunter's EOs and weakly in the Sach's EO of juvenile and adult E. electricus. These results corroborate the fact that the main EO and Hunter's EO have high densities of Na+ channels and produce high voltage discharges while the Sach's EO produces low voltage discharges. More importantly, there were significant differences in kinetic properties of Nka among the three EOs of juvenile E. electricus. The highest and lowest Vmax of Nka were detected in the main EO and the Sach's EO, respectively, with the Hunter's EO having a Vmax value intermediate between the two, indicating that the metabolic costs of EO discharge could be the highest in the main EO. Furthermore, the Nka from the main EO had the lowest Km (or highest affinity) for Na+ and K+ among the three EOs, suggesting that the Nka of the main EO was more effective than those of the other two EOs in maintaining intracellular Na+ and K+ homeostasis and in clearing extracellular K+ after EO discharge.
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Biyun
authors: B
authors: Ching
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Jia M
authors: JM
authors: Woo
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Kum C
authors: KC
authors: Hiong
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Mel V
authors: MV
authors: Boo
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Celine Y L
authors: CY
authors: Choo
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore.
authors: Wai P
authors: WP
authors: Wong
authors: Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616, Republic of Singapore.
authors: Shit F
authors: SF
authors: Chew
authors: Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Republic of Singapore; The Tropical Marine Science Institute, National University of Singapore, Kent Ridge, Singapore, 119227, Republic of Singapore.
authors: Yuen K
authors: YK
authors: Ip
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D004557:Electric Organ / Q000201:enzymology*; D004593:Electrophorus / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D007700:Kinetics; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology*; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D012333:RNA, Messenger; D000254:Sodium-Potassium-Exchanging ATPase