The presence of a Ba ion destabilizes the closed state of the blocked channel by 1.5 kcal/mol, confirming that Ba ions block this channel by binding in the K+-conduction pathway.
Ba ions block voltage-dependent Ca++-activated K+ channels by binding in the K+-conduction pathway, which is inaccessible when the channel is closed.
Voltage-dependent Ca++-activated K+ channels from rat skeletal muscle were reconstituted into planar lipid bilayers, and the kinetics of block of single channels by Ba++ were studied. The Ba++ association rate varies linearly with the probability of the channel being open, while the dissociation rate follows a rectangular hyperbolic relationship with open-state probability. Ba ions can be occluded within the channel by closing the channel with a strongly hyperpolarizing voltage applied during a Ba++-blocked interval. Occluded Ba ions cannot dissociate from the blocking site until after the channel opens. The ability of the closed channel to occlude Ba++ is used as an assay to study the channel's gating equilibrium in the blocked state. The blocked channel opens and closes in a voltage-dependent process similar to that of the unblocked channel. The presence of a Ba ion destabilizes the closed state of the blocked channel, however, by 1.5 kcal/mol. The results confirm that Ba ions block this channel by binding in the K+-conduction pathway. They further show that the blocking site is inaccessible to Ba++ from both the cytoplasmic and external solutions when the channel is closed.
Miller et al. (Tue,) reported a other. Ba++ block vs. Unblocked channel was evaluated on Kinetics of block of single channels by Ba++. The presence of a Ba ion destabilizes the closed state of the blocked channel by 1.5 kcal/mol, confirming that Ba ions block this channel by binding in the K+-conduction pathway.
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