The molecular mechanisms underlying the toxic effects of waterborne free silver (Ag⁺) on freshwater animals are poorly understood. At a holding potential of -60 mV, extracellular short-term application of Ag⁺ ions (1 mM) induced an inward current ([Delta]I_Ag) of 659 ± 43 nA (n = 74; N = 27) in voltage-clamped native Xenopus oocytes. The sulfhydryl reactive N-ethylmaleimide (NEM), potentiated [Delta]I_Ag, whereas L-cysteine abolished the current. Injection of AgNO₃ (1 mM) in order to elevate intracellular Ag⁺ did not affect the baseline current but strongly increased [Delta]I_Ag. To test the involvement of volume regulatory mechanisms we osmotically challenged oocytes prior to Ag⁺ exposure. A preincubation in hypoosmotic bath solution significantly increased [Delta]I_Ag, whereas hyperosmolar conditions decreased [Delta]I_Ag. Further [Delta]I_Ag proved to be sensitive to gadolinium (300 mM Gd ³⁺) which reduced [Delta]I_Ag to 22 ± 2 % (n = 11; N = 2) of the initial response. Taken together, our data suggest that [Delta]I_Ag is elicited by interaction of Ag⁺ ions with extracellular thiol moieties of membrane proteins and this is potentiated by internalized silver. And mechanosensitive non-selective cation channels appear to play a role in the molecular mechanisms that induce [Delta]I_Ag.