Mechanism of branchial apical silver uptake by rainbow trout is via the proton-coupled Na⁺channel

Abstract

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.

Toxicity, bioaccumulation and biomagnification of silver nanoparticles in green algae (Chlorellasp.), water flea (Moina macrocopa), blood worm (Chironomusspp.) and silver barb (Barbonymus gonionotus)

“…Some research has shown that the mode of action of AgNPs on the invertebrate, Caenorhabditis elegans differs from their soluble counterpart, with the NPs affecting the reproduction potential and inducing a high level of oxidative stress (Roh et al, 2009). Ag + can reach the branchial epithelial cells via the Na + channel coupled to the proton ATPase in the apical membrane of the gills, then move to the basolateral membrane of the gill and block the Na + K + ATPtase affecting ion-regulation of Na + Cl -ions across the gill (Fabrega et al, 2011;Bury and Wood 1999). At high concentrations of Ag + , freshwater fish suffer circulatory collapse and death due to blood acidosis (Grosell et al, 1999;Hogstrand and Wood 1998).…”

Silver Nanoparticles as Potential Antibacterial Agents

“…Silver ions or small AgNPs can easily enter the microbial body causing the damage of its intracellular structures. As a consequence ribosomes may be denatured with inhibition of protein synthesis, as well as translation and transcription can be blocked by the binding with the genetic material of the bacterial cell [33,59,60]. Protein synthesis has been shown to be altered by treatment with AgNPs and proteomic data have shown an accumulation of immature precursors of membrane proteins resulting in destabilization of the composition of the outer membrane [61].…”

Histopathological effects of waterborne silver nanoparticles and silver salt on the gills and liver of goldfish Carassius auratus

“…ATPase which affects ionoregulation of Na ? Cl -ions across the gills (Bury and Wood 1999). Ag can also cause tissue damage and accumulate in the liver tissue affecting the ability of fish to cope with low oxygen levels and inducing oxidative stress (Bilberg et al 2010a, b;Scown et al 2010).…”