Biophys J, November 1998, p. 2313-2322, Vol. 75, No. 5

Interaction of Ba²⁺ with the Pores of the Cloned Inward Rectifier K⁺ Channels Kir2.1 Expressed in Xenopus Oocytes

 ^*Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, R.O.C., and  ^#Instituto de Física, Universidad Autónoma de San Luis Potosí, San Luis Potosí, S.L.P. 78000, Mexico

Interactions of Ba²⁺ with K⁺ and molecules contributing to inward rectification were studied in the cloned inward rectifier K⁺ channels, Kir2.1. Extracellular Ba²⁺ blocked Kir2.1 channels with first-order kinetics in a V_m-dependent manner. At V_m more negative than 120 mV, the K_d-V_m relationship became less steep and the dissociation rate constants were larger, suggesting Ba²⁺ dissociation into the extracellular space. Both depolarization and increasing [K⁺]_i accelerated the recovery from extracellular Ba²⁺ blockade. Intracellular K⁺ appears to relieve Ba²⁺ blockade by competitively slowing the Ba²⁺ entrance rate, instead of increasing its exit rate by knocking off action. Intracellular spermine (100 µM) reduced, whereas 1 mM [Mg²⁺]_i only slightly reduced, the ability of intracellular K⁺ to repulse Ba²⁺ from the channel pore. Intracellular Ba²⁺ also blocked outward I_Kir2.1 in a voltage-dependent fashion. At V_m  +40 mV, where intrinsic inactivation is prominent, intracellular Ba²⁺ accelerated the inactivation rate of the outward I_Kir2.1 in a V_m-independent manner, suggesting interaction of Ba²⁺ with the intrinsic gate of Kir2.1 channels.

Biophys J, November 1998, p. 2313-2322, Vol. 75, No. 5
© 1998 by the Biophysical Society   0006-3495/98/11/2313/10  $2.00

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