Departamento de Fisiologia, Setor de Ciências Biológicas, Universidade Federal do Paraná, Curitiba, Paraná, Brazil.
Aquat Toxicol. 2012 Jan 15;106-107:95-103. doi: 10.1016/j.aquatox.2011.10.012. Epub 2011 Oct 28.
Hepatus pudibundus is a strictly marine osmoconformer crab, while Callinectes ornatus inhabits estuarine areas, behaving as a weak hyper-osmoregulator in diluted seawater. Osmoconformers are expected to have higher capacity for cell volume regulation, but gill cells of a regulator are expected to display ion transporters to a higher degree. The influence of lead nitrate (10 μM) on the ability of isolated gill cells from both species to volume regulate under isosmotic and hyposmotic conditions were here evaluated. Without lead, under a 25% hyposmotic shock, the gill cells of both species were quite capable of cell volume maintenance. Cells of C. ornatus, however, had a little swelling (5%) during the hyposmotic shock of greater intensity (50%), while cells of H. pudibundus were still capable of volume regulation. In the presence of lead, even under isosmoticity, the gill cells of both species showed about 10% volume reduction, indicating that lead promotes the loss of water by the cells. When lead was associated with 25% and 50% hyposmotic shock, C. ornatus cells lost more volume (15%), when compared to isosmotic conditions, while H. pudibundus cells showed volume regulation. We then analyzed the possible ways of action of lead on the mechanisms of cell volume regulation in the two species. Verapamil (100 μM) was used to inhibit Ca²⁺ channels, ouabain (100 μM) to inhibit Na⁺/K⁺-ATPase, and HgCl₂ (100 μM) to inhibit aquaporins. Our results suggest that: (1) Ca²⁺ channels are candidates for lead entry into gill cells of H. pudibundus and C. ornatus, being the target of lead action in these cells; (2) aquaporins are much more relevant for water flux in H. pudibundus; and (3) the Na⁺/K⁺-ATPase is much more relevant for volume regulation in C. ornatus. Osmoregulators may be more susceptible to metal contamination than osmoconformers, especially in situations of reduced salinity, for two basic reasons: (1) lower capacity of volume regulation and (2) putative higher uptake of Pb²⁺ through ionic pathways that operate in salt absorption, such as, for example, the Na⁺/K⁺-ATPase.
软壳青蟹是一种严格的海洋等渗调节生物，而三疣梭子蟹则栖息在河口地区，在稀释海水中表现出较弱的超渗调节能力。等渗生物预计具有更高的细胞体积调节能力，但调节器的鳃细胞预计会表现出更高程度的离子转运蛋白。本文在此评估了硝酸铅（10 μM）对这两种物种的分离鳃细胞在等渗和低渗条件下调节体积的能力的影响。在没有铅的情况下，在 25%的低渗冲击下，两种物种的鳃细胞都能够很好地维持细胞体积。然而，在更强烈的 50%低渗冲击下，三疣梭子蟹的细胞有轻微肿胀（5%），而软壳青蟹的细胞仍能进行体积调节。在铅的存在下，即使在等渗条件下，两种物种的鳃细胞也显示出约 10%的体积减少，表明铅促进了细胞失水。当铅与 25%和 50%的低渗冲击相结合时，与等渗条件相比，三疣梭子蟹细胞失去了更多的体积（15%），而软壳青蟹细胞则显示出体积调节。然后，我们分析了铅对两种物种细胞体积调节机制作用的可能方式。我们使用维拉帕米（100 μM）抑制 Ca²⁺通道，哇巴因（100 μM）抑制 Na⁺/K⁺-ATP 酶，氯化汞（100 μM）抑制水通道蛋白。我们的结果表明：（1）Ca²⁺通道是铅进入软壳青蟹和三疣梭子蟹鳃细胞的候选途径，是这些细胞中铅作用的靶点；（2）水通道蛋白对于软壳青蟹的水通量更为重要；（3）Na⁺/K⁺-ATP 酶对于三疣梭子蟹的体积调节更为重要。与等渗生物相比，渗透调节生物可能更容易受到金属污染的影响，尤其是在盐度降低的情况下，原因有两个：（1）体积调节能力较低；（2）通过在盐吸收中起作用的离子途径（例如，Na⁺/K⁺-ATP 酶），可能会吸收更多的 Pb²⁺。
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