Hernández-R J
Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y de Estudios Avanzados, México, D.F.
Neurochem Int. 1992 Jan;20(1):1-10. doi: 10.1016/0197-0186(92)90119-c.
A long period of experimental work has led to the conclusion that Na+/K(+)-ATPase is the enzymatic version of the Na+/K+ pump. This enzymatic system is in charge of various important cell functions. Among them cationic equilibrium and recovering of resting membrane potential in neurons is relevant. A tetrameric ensemble of peptides conform the system known as alpha and beta subunits. The alpha subunit is subdivided in alpha 1, alpha 2 and alpha 3, according to different location and properties. Regulatory factors intrinsic to the Na+/K(+)-ATPase system are: ATP, Na+ and Mg2+ concentrations inside the cell, and K+ outside. The enzyme activity is also regulated by extrinsic factors like some hormones (insulin and thyroxine). Induction of gene expression or post-translational modifications of the preexisting pool of the enzyme are the basic mechanisms of regulation proposed. Other extrinsic factors that seem to regulate the enzyme activity are some neurotransmitters. Among them the most extensively studied are catecholamines, mainly norepinephrine (NE) and lately serotonin (5-HT). The mechanism suggested for NE activation of the enzyme seems to involve specific receptors or a non-specific chelating action related to the catechol group that would relieve the inhibition by divalent cations. Another possibility is that NE removes an endogenous inhibitory factor present in the cytoplasm. The Na+/K(+)-ATPase is activated also by 5-HT. In vivo pharmacological and nutriological manipulations of brain 5-HT are accompanied by parallel responses of Na+/K(+)-ATPase activity. Serotonin agonists do activate the enzyme and antagonists neutralize the activation. In vitro there is a different dose dependent activation, according to the brain region. The mechanism involved seems to implicate a specific receptor system. Serotonin-Na+/K(+)-ATPase interaction in the rat brain is probably of functional relevance because it disappears in amygdaloid kindling. Also it seems to influence the ionic regulation of the pigment transport mechanism in crayfish photoreceptors. In relation to other neurotransmitters, a weak response to histamine was observed with acetylcholine, GABA and glutamic acid, the results were negative.
Na+/K(+)-ATP酶是Na+/K+泵的酶形式。这个酶系统负责各种重要的细胞功能。其中阳离子平衡以及神经元静息膜电位的恢复与之相关。该系统由称为α和β亚基的肽的四聚体组成。根据不同的位置和性质，α亚基又细分为α1、α2和α3。Na+/K(+)-ATP酶系统的内在调节因子包括：细胞内的ATP、Na+和Mg2+浓度，以及细胞外的K+。酶的活性也受诸如某些激素（胰岛素和甲状腺素）等外在因素的调节。基因表达的诱导或酶的现有库的翻译后修饰是所提出的基本调节机制。其他似乎调节酶活性的外在因素是一些神经递质。其中研究最广泛的是儿茶酚胺，主要是去甲肾上腺素（NE），最近还有5-羟色胺（5-HT）。所提出的NE激活该酶的机制似乎涉及特定受体或与儿茶酚基团相关的非特异性螯合作用，这将减轻二价阳离子的抑制作用。另一种可能性是NE去除细胞质中存在的内源性抑制因子。5-HT也能激活Na+/K(+)-ATP酶。对大脑5-HT进行体内药理学和营养学操作时，Na+/K(+)-ATP酶活性会产生相应的平行反应。5-羟色胺激动剂确实能激活该酶，而拮抗剂则能中和这种激活作用。在体外，根据脑区不同存在不同的剂量依赖性激活。所涉及的机制似乎与特定的受体系统有关。大鼠脑中5-羟色胺与Na+/K(+)-ATP酶的相互作用可能具有功能相关性，因为在杏仁核点燃时这种相互作用会消失。它似乎也会影响小龙虾光感受器中色素转运机制的离子调节。关于其他神经递质，观察到组胺、乙酰胆碱、γ-氨基丁酸和谷氨酸的反应较弱，结果为阴性。
