Department of Biochemistry, Kyorin University School of Medicine, Shinkawa 6-20-2, Mitaka, Tokyo 181-8611, Japan.
J Insect Physiol. 2013 Mar;59(3):332-8. doi: 10.1016/j.jinsphys.2012.12.002. Epub 2012 Dec 26.
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.
在哺乳动物的血液中，钠离子浓度高于钾离子浓度，而在鳞翅目昆虫的血淋巴中，钾离子浓度高于钠离子浓度。钠钾-ATP 酶调节哺乳动物血液中的钠离子和钾离子浓度。因此，在鳞翅目昆虫中，钠钾-ATP 酶的缺失是可以预期的。然而，我们观察到，在鳞翅目昆虫家蚕幼虫的神经组织中，钠钾-ATP 酶非常丰富。此外，我们发现，尽管家蚕幼虫的血淋巴中钙离子浓度非常高（30-50mM），但 3mM 的钙离子可以完全抑制家蚕钠钾-ATP 酶的体外活性（Homareda，2010 年）。为了研究家蚕钠钾-ATP 酶在体内不受钙离子抑制的原因，我们使用免疫组织化学技术观察了神经组织中钠钾-ATP 酶的定位。钠钾-ATP 酶分布在皮层和神经丛中，但不在家蚕大脑的神经鞘中，而质膜钙泵似乎分布在神经鞘和皮层及神经丛中。这些结果表明，神经元钠钾-ATP 酶可能被具有质膜钙泵的血脑屏障所保护，免受高钙离子浓度的影响。
