Localization of Na(+)/K(+)-ATPase in silkworm brain: a possible mechanism for protection of Na(+)/K(+)-ATPase from Ca(2+)

• Published in: Journal of insect physiology Vol. 59; no. 3; pp. 332 - 338
• Main Authors: Homareda, Haruo, Otsu, Masahiro
• Format: Journal Article
• Language: English
• Published: England 01.03.2013
• Subjects: Animals; Bombyx - enzymology; Bombyx - metabolism; Brain - enzymology; Brain - metabolism; Calcium - metabolism; Enzyme Inhibitors - metabolism; Insect Proteins - metabolism; Nerve Tissue - enzymology; Protein Transport; Sodium-Potassium-Exchanging ATPase - metabolism
• ISSN: 1879-1611
• DOI: 10.1016/j.jinsphys.2012.12.002

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.