abstract
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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/(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/(Kir2.1) in a V(m)- independent manner, suggesting interaction of Ba2 with the intrinsic gate of Kir2.1 channels.
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Interactions of Ba2%2b with K%2b and molecules contributing to inward rectification were studied in the cloned inward rectifier K%2b channels, Kir2.1. Extracellular Ba2%2b 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%2b dissociation into the extracellular space. Both depolarization and increasing [K%2b](i) accelerated the recovery from extracellular Ba2%2b blockade. Intracellular K%2b appears to relieve Ba2%2b blockade by competitively slowing the Ba2%2b entrance rate, instead of increasing its exit rate by knocking off action. Intracellular spermine (100 μM) reduced, whereas 1 mM [Mg2%2b](i) only slightly reduced, the ability of intracellular K%2b to repulse Ba2%2b from the channel pore. Intracellular Ba2%2b also blocked outward/(Kir2.1) in a voltage-dependent fashion. At V(m) ≥ %2b40 mV, where intrinsic inactivation is prominent, intracellular Ba2%2b accelerated the inactivation rate of the outward/(Kir2.1) in a V(m)- independent manner, suggesting interaction of Ba2%2b with the intrinsic gate of Kir2.1 channels.
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