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Slow gating charge immobilization in the human potassium channel Kv1.5 and its prevention by 4‐aminopyridine.
Author(s) -
Fedida D,
Bouchard R,
Chen F S
Publication year - 1996
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1996.sp021499
Subject(s) - 4 aminopyridine , tetraethylammonium chloride , gating , chemistry , tetraethylammonium , biophysics , repolarization , potassium channel , potassium channel blocker , depolarization , hek 293 cells , intracellular , patch clamp , potassium , electrophysiology , biochemistry , medicine , biology , receptor , organic chemistry
1. The relationship between ionic current inactivation and immobilization of ‘off'‐gating charge in human Kv1.5 channels expressed in human embryonic kidney (HEK293) cells was studied using 4‐aminopyridine (4‐AP) and tetraethylammonium chloride (TEA‐Cl). 2. The charge transferred during short (< 10 ms) depolarizations (Q(on)) was conserved on repolarization (Q(off)) although peak off‐gating current (off‐Ig) was reduced and the time course prolonged (tau decay increased from 0.4 to > 1.2 ms). For +80 mV pulses longer than 50 ms, Q(off) at 20 ms was less than Q(on) (Q(off)/Q(on) ratio was 0.26 +/‐ 0.06 at 450 ms). We attribute this to a relative ‘immobilization’ of gating charge during long depolarizations. 3. 4‐AP (0.1‐1 mM) prevented slowing of off‐Ig, allowing saturation of peak off‐Ig. 4‐AP also completely prevented immobilization of off‐Ig after long depolarizations. In 1 mM 4‐AP, off‐Ig waveforms decayed rapidly and the charge ratio Q(off)/Q(on) remained at 1.0. 4. In addition to its effects on Ig, 1 mM 4‐AP prevented the slow inactivation of ionic current seen during strong depolarizations. An initial block was caused by 4‐AP or 1 mM intracellular TEA internally applied. However, only 4‐AP prevented the slower, later development of C‐type inactivation. 5. We suggest that slow current inactivation is accompanied by a gating charge immobilization in Kv1.5. 4‐AP potently inhibits the changes in Q(off)/Q(on0, off‐Ig, and ionic currents that underlie slow inactivation. Some actions of 4‐AP appear independent of its properties as a blocker of open K+ channels, and are not mimicked by internal TEA.