Bury N R, Wood C M
Department of Biological Sciences, Hatherly Laboratories, University of Exeter, Exeter, United Kingdom EX4 4PS.
Am J Physiol. 1999 Nov;277(5):R1385-91. doi: 10.1152/ajpregu.1999.277.5.R1385.
The branchial uptake mechanism of the nonessential heavy metal silver from very dilute media by the gills of freshwater rainbow trout was investigated. At concentrations >36 nM AgNO(3), silver rapidly entered the gills, reaching a peak at 1 h, after which time there was a steady decline in gill silver concentration and a resulting increase in body silver accumulation. Below 36 nM AgNO(3), there was only a very gradual increase in gill and body silver concentration over the 48-h exposure period. Increasing water sodium concentration ([Na(+)]; 0.05 to 21 mM) significantly reduced silver uptake, although, in contrast, increasing ambient [Ca(2+)] or [K(+)] up to 10 mM did not reduce silver uptake. Kinetic analysis of silver uptake at varying [Na(+)] showed a significant decrease in maximal silver transport capacity (173 +/- 34 pmol. g(-1). h(-1) at 0.1 mM [Na(+)] compared with 35 +/- 9 at 13 mM [Na(+)]) and only a slight decrease in the affinity for silver transport (K(m); 55 +/- 27 nM at 0.1 mM [Na(+)] compared with 91 +/- 47 nM at 13 mM [Na(+)]). Phenamil (a specific blocker of Na(+) channels), at a concentration of 100 microM, blocked Na(+) uptake by 78% of control values (58% after washout), and bafilomycin A(1) (a specific blocker of V-type ATPase), at a concentration of 2 microM, inhibited Na(+) uptake by 57% of control values, demonstrating the presence of a proton-coupled Na(+) channel in the apical membrane of the gills. Phenamil (after washout) and bafilomycin A(1) also blocked silver uptake by 62 and 79% of control values, respectively, indicating that Ag(+) is able to enter the apical membrane via the proton-coupled Na(+) channel.
研究了淡水虹鳟鱼鳃从极稀介质中摄取非必需重金属银的鳃摄取机制。在硝酸银浓度>36 nM时，银迅速进入鳃，1小时时达到峰值，此后鳃中银浓度稳步下降，鱼体银积累量增加。在36 nM硝酸银以下，在48小时的暴露期内，鳃和鱼体中的银浓度仅非常缓慢地增加。增加水体钠浓度（[Na⁺]；0.05至21 mM）显著降低银的摄取，然而，相比之下，将环境中的[Ca²⁺]或[K⁺]增加至10 mM并不会降低银的摄取。对不同[Na⁺]下银摄取的动力学分析表明，最大银转运能力显著降低（在0.1 mM [Na⁺]时为173±34 pmol·g⁻¹·h⁻¹，而在13 mM [Na⁺]时为35±9），并且银转运亲和力（Kₘ）仅略有降低（在0.1 mM [Na⁺]时为55±27 nM，而在13 mM [Na⁺]时为91±47 nM）。浓度为100 μM的非那明（一种Na⁺通道特异性阻滞剂）使Na⁺摄取量比对照值降低78%（洗脱后为58%），浓度为2 μM的巴弗洛霉素A₁（一种V型ATP酶特异性阻滞剂）使Na⁺摄取量比对照值降低57%，这表明鳃顶膜中存在质子偶联Na⁺通道。非那明（洗脱后）和巴弗洛霉素A₁也分别使银摄取量比对照值降低62%和79%，表明Ag⁺能够通过质子偶联Na⁺通道进入顶膜。
