Biophys J, May 1998, p. 2318-2326, Vol. 74, No. 5

Interaction of Permeant and Blocking Ions in Cloned Inward-Rectifier K⁺ Channels

 ^*Department of Otolaryngology and  ^#Institute of Physiology, University of Tübingen, D-72076 Tübingen, Germany

Blocking cloned inward-rectifier potassium (K_ir) channels from the cytoplasmic side was analyzed with a rapid application system exchanging the intracellular solution on giant inside-out patches from Xenopus oocytes in <2 ms. Dependence of the pore-block on interaction of the blocking molecule with permeant and impermeant ions on either side of the membrane was investigated in K_ir1.1 (ROMK1) channels blocked by ammonium derivatives and in K_ir4.1 (BIR10) channels blocked by spermine. The blocking reaction in both systems showed first-order kinetics and allowed separate determination of on- and off-rates. The off-rates of block were strongly dependent on the concentration of internal and external bulk ions, but almost independent of the ion species at the cytoplasmic side of the membrane. With K⁺ as the only cation on both sides of the membrane, off-rates exhibited strong coupling to the K⁺ reversal potential (E_K) and increased and decreased with reduction in intra and extracellular K⁺ concentration, respectively. The on-rates showed significant dependence on concentration and species of internal bulk ions. This control of rate-constants by interaction of permeant and impermeant internal and external ions governs the steady-state current-voltage relation (I-V) of K_ir channels and determines their physiological function under various conditions.

Biophys J, May 1998, p. 2318-2326, Vol. 74, No. 5
© 1998 by the Biophysical Society   0006-3495/98/05/2318/09  $2.00

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