Cu~(2+) reveals different binding sites of amiloride and CDPC on the apical Na channel of frog skin

摘要

The effect of Cu~(2+) ions, present in the mucosal bathing solution, on the transepithelial short-circuit current (I_(sc)) and conductance (G_t) and on the blocker-induced noise of apical Na channels, was studied on the isolated ventral skin of the frog Rana temporaria. Cu~(2+) effects were concentration-dependent, the full effect being reached at 50 μmol/l. Cu~(2+) increased I_(sc) and G_t; this effect was eliminated by high concentrations of amiloride (30 μmol/l) and of CDPC (150 μmol/l). Cu~(2+) markedly reduced the corner frequency (f_c) of the Na channel noise, while having virtually no effect on the f_c of CDPC-induced noise. Cu~(2+) reduces the association rate constant of amiloride to the Na channel to one third; this effect is interpreted as indicating competition between Cu~(2+) and amiloride for the same (negatively charged) binding site on the channel, while CDPC appears to bind on a different site.