Matsuo Aline Y O, Playle Richard C, Val Adalberto L, Wood Chris M
Laboratory of Ecophysiology and Molecular Evolution, Instituto Nacional de Pesquisas da Amazônia (INPA), Alameda Cosme Ferreira, 1756--Aleixo, 69083-000, Manaus, AM, Brazil.
Aquat Toxicol. 2004 Oct 18;70(1):63-81. doi: 10.1016/j.aquatox.2004.07.005.
We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na+) transport in juvenile Oncorhynchus mykiss (approximately 2.5 g) in the presence and absence of simultaneous acute exposure to copper (Cu2+; 0, 70, and 300 microg l(-1)). Trout were acclimated in either hardwater (approximately 1000 microM Ca2+) or softwater (approximately 100 microM Ca2+), and DOM was tested at approximately 8 mg C l(-1) using a natural (NOM) and a commercial (AHA) source. Ion transport was evaluated based on kinetics estimates (maximum Na+ uptake rates, Jmax; substrate affinity, Km) and unidirectional flux measurements (Jin, Jout, Jnet). Jmax was higher and unidirectional flux rates were greater in softwater-acclimated trout. Fish exposed to DOM alone in hardwater exhibited an increased Na+ transport capacity indicated by both the kinetics (67% higher Jmax for AHA) and Jin measurements (153% higher for AHA and 125% higher for NOM). In softwater, the effects of DOM alone on kinetic parameters and unidirectional flux rates were negligible. Cu2+ affected Na+ uptake by a mixed-type inhibition (both non-competitive and competitive). In hardwater, only Km was increased (i.e., affinity decreased), whereas in softwater, Km was increased and Jmax was decreased, with more marked effects at the higher Cu2+ level. In hardwater, the stimulatory effect of AHA on Jmax persisted even in the presence of 300 microg l(-1) Cu2+, whereas both AHA and NOM prevented the increase in Km caused by Cu2+; these effects were reflected in Jin measurements. In softwater, AHA helped to protect against the increased Km caused by high Cu2+, but there was no protection against the inhibition of Jmax. Unidirectional flux measurements indicated that in softwater, Cu2+ inhibited Jin at 70 microg l(-1), whereas at 300 microg l(-1) Cu2+, Jout was also stimulated. Fish were more affected by Cu2+ in softwater, as indicated by the inability to control diffusive losses of Na+ and a reduced ability to take up Na+, but in the presence of DOM, losses were better controlled at the end of 6 h exposure. We conclude that DOM has direct effects on the gills, as well as protecting fish against acute Cu2+ toxicity. This occurs because DOM complexes Cu2+, and because it acts on the transport and permeability properties of the gills. These effects differ depending on both water hardness and the nature of the DOM source.
我们研究了在同时存在和不存在急性铜（Cu2+；0、70和300微克/升）暴露的情况下，溶解有机物（DOM）对虹鳟幼鱼（约2.5克）钠（Na+）转运的生理影响。虹鳟在硬水（约1000微摩尔/升Ca2+）或软水（约100微摩尔/升Ca2+）中驯化，使用天然（NOM）和商业（AHA）来源的DOM，在约8毫克碳/升的浓度下进行测试。基于动力学估计（最大Na+摄取率，Jmax；底物亲和力，Km）和单向通量测量（Jin、Jout、Jnet）评估离子转运。在软水驯化的虹鳟中，Jmax更高，单向通量率更大。在硬水中单独暴露于DOM的鱼表现出Na+转运能力增加，这在动力学（AHA的Jmax高67%）和Jin测量（AHA高153%，NOM高125%）中均有体现。在软水中，单独的DOM对动力学参数和单向通量率的影响可忽略不计。Cu2+通过混合型抑制（非竞争性和竞争性）影响Na+摄取。在硬水中，仅Km增加（即亲和力降低），而在软水中，Km增加且Jmax降低，在较高Cu2+水平时影响更明显。在硬水中，即使存在300微克/升的Cu2+，AHA对Jmax的刺激作用仍然存在，而AHA和NOM均能防止Cu2+引起的Km增加；这些影响在Jin测量中得到体现。在软水中，AHA有助于防止高Cu2+引起的Km增加，但对Jmax的抑制没有保护作用。单向通量测量表明，在软水中，70微克/升的Cu2+抑制Jin，而在300微克/升的Cu2+时，Jout也受到刺激。虹鳟在软水中受Cu2+的影响更大，表现为无法控制Na+的扩散损失以及摄取Na+的能力降低，但在存在DOM的情况下，在6小时暴露结束时损失得到更好的控制。我们得出结论，DOM对鳃有直接影响，同时保护鱼类免受急性Cu2+毒性。这是因为DOM与Cu2+络合，并且它作用于鳃的转运和通透性特性。这些影响因水硬度和DOM来源的性质而异。
