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Biophys J, November 2000, p. 2416-2433, Vol. 79, No. 5
Department of Physiology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
Na+ conductance through cloned K+
channels has previously allowed characterization of inactivation and
K+ binding within the pore, and here we have used
Na+ permeation to study recovery from C-type inactivation
in human Kv1.5 channels. Replacing K+ in the solutions with
Na+ allows complete Kv1.5 inactivation and alters the
recovery. The inactivated state is nonconducting for K+ but
has a Na+ conductance of 13% of the open state. During
recovery, inactivated channels progress to a higher Na+
conductance state (R) in a voltage-dependent manner before deactivating to closed-inactivated states. Channels finally recover from
inactivation in the closed configuration. In the R state channels can
be reactivated and exhibit supernormal Na+ currents with a
slow biexponential inactivation. Results suggest two pathways for entry
to the inactivated state and a pore conformation, perhaps with a higher
Na+ affinity than the open state. The rate of recovery from
inactivation is modulated by Na+o such that 135 mM Na+o promotes the recovery to normal closed,
rather than closed-inactivated states. A kinetic model of recovery that
assumes a highly Na+-permeable state and deactivation to
closed-inactivated and normal closed states at negative voltages can
account for the results. Thus these data offer insight into how Kv1.5
channels recover their resting conformation after inactivation and how
ionic conditions can modify recovery rates and pathways.
Biophys J, November 2000, p. 2416-2433, Vol. 79, No. 5
© 2000 by the Biophysical Society 0006-3495/00/11/2416/18 $2.00
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