title: Short-term exposure to waterborne free silver has acute effects on membrane current of Xenopus oocytes.
abstract: Waterborne free silver can cause osmo- and ionoregulatory disturbances in freshwater organisms. The effects of a short-term exposure to extracellular Ag+ ions on membrane currents were investigated in voltage-clamped defolliculated Xenopus oocytes. At a holding potential of -60 mV, ionic silver (1 microM Ag+) increased inward currents (=I(Ag)) from -8+/-2 nA to -665+/-41 nA (n=74; N=27). I(Ag) activated within 2 min of silver exposure and then rose impetuously. This current was largely reversible by washout and repeatable. I(Ag) reversed around -30 mV and rectified slightly at more positive potentials. Na+-free bath conditions reduced the silver-induced current to a smaller but sustained current. The response to silver was abolished by the Cl- channel blockers DIDS and SITS, whereas niflumic acid strongly potentiated I(Ag). Intraoocyte injection of AgNO3 to about 1 mM [Ag]i strongly potentiated I(Ag). Extracellular application of either dithiothreitol (DTT), a compound known to reduce disulfide bridges, or L-cysteine abolished Ag+-activated increase of membrane current. In contrast, n-ethylmaleimide (NEM) which oxidizes SH-groups potentiated I(Ag). Hypoosmotic bath solution significantly increased I(Ag) whereas hyperosmolar conditions attenuated I(Ag). The activation of I(Ag) was largely preserved after chelation of cytosolic Ca2+ ions with BAPTA/AM. Taken together, these data suggest that Xenopus oocytes are sensitive to short-term exposure to waterborne Ag+ ions and that the elicited membrane currents result from extra- and intracellular action of Ag+ ions on peptide moieties at the oocyte membrane but may also affect conductances after internalization.
authors.affiliation: Department of Internal Medicine, Physiology and Biophysics, University of Iowa, College of Medicine, 500 EMRB, Iowa City, IA 52242, USA. mikael.schnizler@uiowa.edu
authors.forename: Mikael K
authors.initials: MK
authors.lastname: Schnizler
authors.forename: Roman
authors.initials: R
authors.lastname: Bogdan
authors.forename: Anke
authors.initials: A
authors.lastname: Bennert
authors.forename: Nicolas R
authors.initials: NR
authors.lastname: Bury
authors.forename: Martin
authors.initials: M
authors.lastname: Fronius
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Clauss
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane; D002712:Chlorides / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D009995:Osmosis; D018408:Patch-Clamp Techniques; D012834:Silver / Q000494:pharmacology*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D002712:Chlorides; D007473:Ion Channels; D012834:Silver; D002118:Calcium