Silva Virgília S, Duarte Ana I, Rego A Cristina, Oliveira Catarina R, Gonçalves Paula P
Centro de Estudos do Ambiente e Mar, Departamento de Biologia, Universidade de Aveiro, Portugal.
Toxicol Sci. 2005 Dec;88(2):485-94. doi: 10.1093/toxsci/kfi324. Epub 2005 Sep 14.
The ability of aluminum to inhibit the (Na(+)/K(+))ATPase activity has been observed by several investigators. The (Na(+)/K(+))ATPase is characterized by a complex molecular heterogeneity that results from the expression and differential association of multiple isoforms of both catalytic (alpha) and regulatory (beta) subunits. For instance, three main alpha (alpha(1), alpha(2) and alpha(3)) and three beta (beta(1), beta(2) and beta(3)) subunit isoforms exist in vertebrate nervous tissue, whereas only alpha(1) and beta(1) have been identified in kidney. However, no studies have focused on determining the change in (Na(+)/K(+))ATPase isoforms caused by chronic exposure to aluminum and its relation with aluminum toxicity. In this study, adult male Wistar rats were submitted to chronic dietary AlCl(3) exposure (0.03 g/day of AlCl(3) for 4 months), and the activity and protein expression of (Na(+)/K(+))ATPase isozymes were studied in brain cortex synaptosomes and in kidney homogenates. The intracellular levels of adenine nucleotides, plasma membrane integrity, and aluminum accumulation were also studied in brain synaptosomes. Aluminum accumulation upon chronic dietary AlCl(3) administration significantly decreased the (Na(+)/K(+))ATPase activity measured in the presence of nonlimiting Mg-ATP concentrations, without compromising protein expression of alpha-subunit isoforms in brain and kidney. Aluminum-induced synaptosomal (Na(+)/K(+))ATPase inhibition was due to a reduction in the activity of isozymes containing alpha(1)-alpha(2) and alpha(3)-subunits. The onset of enzyme inhibition was accompanied by a decrease of the (Na(+)/K(+))ATPase sensitivity to submicromolar concentrations of ouabain, and it preceded major damage in plasma membrane integrity and energy supply, as revealed by the analysis of lactate dehydrogenase leakage and endogenous adenine nucleotides. The data suggest that, during chronic dietary exposure to AlCl(3), brain (Na(+)/K(+))ATPase activity drops, even if no significant alterations of catalytic subunit protein expression, cellular energy depletion, and changes in cell membrane integrity are observed. Implications regarding underlying mechanisms of aluminum neurotoxicity are discussed.
几位研究者已观察到铝抑制（Na⁺/K⁺）ATP酶活性的能力。（Na⁺/K⁺）ATP酶的特征是具有复杂的分子异质性，这是由催化（α）亚基和调节（β）亚基的多种同工型的表达及差异结合所导致的。例如，在脊椎动物神经组织中存在三种主要的α（α₁、α₂和α₃）亚基和三种β（β₁、β₂和β₃）亚基同工型，而在肾脏中仅鉴定出α₁和β₁。然而，尚无研究聚焦于确定长期暴露于铝所导致的（Na⁺/K⁺）ATP酶同工型的变化及其与铝毒性的关系。在本研究中，成年雄性Wistar大鼠接受长期饮食中AlCl₃暴露（每天0.03 g AlCl₃，持续4个月），并研究了大脑皮质突触体和肾脏匀浆中（Na⁺/K⁺）ATP酶同工酶的活性和蛋白质表达。还研究了大脑突触体中腺嘌呤核苷酸的细胞内水平、质膜完整性和铝蓄积情况。长期给予饮食中的AlCl₃后铝蓄积显著降低了在非限制性Mg - ATP浓度存在下测得的（Na⁺/K⁺）ATP酶活性，而未影响大脑和肾脏中α亚基同工型的蛋白质表达。铝诱导的突触体（Na⁺/K⁺）ATP酶抑制是由于含有α₁ - α₂和α₃亚基的同工酶活性降低。酶抑制的发生伴随着（Na⁺/K⁺）ATP酶对亚微摩尔浓度哇巴因敏感性的降低，并且在质膜完整性和能量供应出现重大损伤之前就已发生，这通过乳酸脱氢酶泄漏和内源性腺嘌呤核苷酸的分析得以揭示。数据表明，在长期饮食暴露于AlCl₃期间，大脑（Na⁺/K⁺）ATP酶活性下降，即使未观察到催化亚基蛋白质表达的显著改变、细胞能量耗竭和细胞膜完整性的变化。文中讨论了关于铝神经毒性潜在机制的相关问题。
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