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1.3
-subunit affect voltage-dependent gating
Departments of 1 Pharmacology, 2 Molecular Physiology and Biophysics, and 3 Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
The Kv
1.3 subunit confers a voltage-dependent, partial
inactivation (time constant = 5.76 ± 0.14 ms at +50 mV), an
enhanced slow inactivation, a hyperpolarizing shift in the activation
midpoint, and an increase in the deactivation time constant of the
Kv1.5 delayed rectifier. Removal of the first 10 amino acids from
Kv1.3 eliminated the effects on fast and slow inactivation but not
the voltage shift in activation. Addition of the first 87 amino acids of Kv1.3 to the amino terminus of Kv1.5 reconstituted fast and slow
inactivation without altering the midpoint of activation. Although an
internal pore mutation that alters quinidine block (V512A) did not
affect Kv1.3-mediated inactivation, a mutation of the external mouth
of the pore (R485Y) increased the extent of fast inactivation while
preventing the enhancement of slow inactivation. These data suggest
that 1) Kv1.3-mediated effects involve at least two distinct domains of this -subunit,
2) inactivation involves open
channel block that is allosterically linked to the external pore, and
3) the Kv1.3-induced shift in the
activation midpoint is functionally distinct from inactivation.
Shaker-like potassium channel; N-type inactivation; C-type inactivation
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