title: Localization of Na(+)/K(+)-ATPase in silkworm brain: a possible mechanism for protection of Na(+)/K(+)-ATPase from Ca(2+).
abstract: In mammalian blood, the Na(+) concentration is higher than the K(+) concentration, whereas in hemolymph of lepidopterous insects, the K(+) concentration is higher than the Na(+) concentration. Na(+)/K(+)-ATPase regulates Na(+) and K(+) concentrations in mammalian blood. Therefore, the absence of Na(+)/K(+)-ATPase in lepidopterous insects might be expected. However, we have observed that Na(+)/K(+)-ATPase is abundant in nerve tissues of larvae of silkworm, a lepidopterous insect. Furthermore, we found that silkworm Na(+)/K(+)-ATPase was completely inhibited by 3 mM Ca(2+)in vitro (Homareda, 2010), although the Ca(2+) concentration is very high (30-50 mM) in the hemolymph of silkworm larvae. To investigate the reason why silkworm Na(+)/K(+)-ATPase is not inhibited by Ca(2+)in vivo, we observed the localization of Na(+)/K(+)-ATPase in nerve tissues using immunohistochemical techniques. Na(+)/K(+)-ATPase was distributed in the cortex and neuropile but not in the perineurium of the silkworm brain, while plasma membrane Ca(2+)-ATPase appeared to distribute in the perineurium as well as in the cortex and neuropile. These results support a possibility that neuronal Na(+)/K(+)-ATPase is protected from a high Ca(2+) concentration by the blood-brain barrier consisting of perineurial glial cells with plasma membrane Ca(2+)-ATPase.
authors.affiliation: Department of Biochemistry, Kyorin University School of Medicine, Shinkawa 6-20-2, Mitaka, Tokyo 181-8611, Japan. homareda@ks.kyorin-u.ac.jp
authors.forename: Haruo
authors.initials: H
authors.lastname: Homareda
authors.forename: Masahiro
authors.initials: M
authors.lastname: Otsu
mesh_terms: D000818:Animals; D012831:Bombyx / Q000201:enzymology* / Q000378:metabolism; D001921:Brain / Q000201:enzymology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism*; D009417:Nerve Tissue / Q000201:enzymology; D021381:Protein Transport; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D019476:Insect Proteins; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium