title: Cu2+ reveals different binding sites of amiloride and CDPC on the apical Na channel of frog skin.
abstract: The effect of Cu2+ ions, present in the mucosal bathing solution, on the transepithelial short-circuit current (Isc) and conductance (Gt) and on the blocker-induced noise of apical Na channels, was studied on the isolated ventral skin of the frog Rana temporaria. Cu2+ effects were concentration-dependent, the full effect being reached at 50 micromol/l. Cu2+ increased Isc and Gt; this effect was eliminated by high concentrations of amiloride (30 micromol/l) and of CDPC (150 micromol/l). Cu2+ markedly reduced the corner frequency (fc) of the Na channel noise, while having virtually no effect on the fc of CDPC-induced noise. Cu2+ reduces the association rate constant of amiloride to the Na channel to one third; this effect is interpreted as indicating competition between Cu2+ and amiloride for the same (negatively charged) binding site on the channel, while CDPC appears to bind on a different site.
authors.affiliation: Laboratorium voor Fysiologie, K.U.Leuven, Campus Gasthuisberg, B- 3000 Leuven, Belgium. flonta@bio.bio.unibuc.ro
authors.forename: M L
authors.initials: ML
authors.lastname: Flonta
authors.forename: J D
authors.initials: JD
authors.lastname: Beir-Simaels
authors.forename: D
authors.initials: D
authors.lastname: Mesotten
authors.forename: W
authors.initials: W
authors.lastname: Van Driessche
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive / Q000187:drug effects; D003300:Copper / Q000494:pharmacology*; D004553:Electric Conductivity; D015640:Ion Channel Gating / Q000187:drug effects; D011896:Rana temporaria; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015222:Sodium Channels; C058206:6-chloro-3,5-diaminopyrazine-3-carboxamide; C042514:cuprous ion; D003300:Copper; D000584:Amiloride