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Chloride dependence of hyperpolarization‐activated chloride channel gates
Author(s) -
Pusch Michael,
Jordt SvenEric,
Stein Valentin,
Jentsch Thomas J.
Publication year - 1999
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 - 10.1111/j.1469-7793.1999.341ac.x
Subject(s) - hyperpolarization (physics) , gating , chemistry , chloride channel , membrane potential , mutant , xenopus , biophysics , crystallography , stereochemistry , biochemistry , biology , nuclear magnetic resonance spectroscopy , gene
1 ClC proteins are a class of voltage‐dependent Cl − channels with several members mutated in human diseases. The prototype ClC‐0 Torpedo channel is a dimeric protein; each subunit forms a pore that can gate independently from the other one. A common slower gating mechanism acts on both pores simultaneously; slow gating activates ClC‐0 at hyperpolarized voltages. The ClC‐2 Cl − channel is also activated by hyperpolarization, as are some ClC‐1 mutants (e.g. D136G) and wild‐type (WT) ClC‐1 at certain pH values. 2 We studied the dependence on internal Cl − ([Cl − ] i ) of the hyperpolarization‐activated gates of several ClC channels (WT ClC‐0, ClC‐0 mutant P522G, ClC‐1 mutant D136G and an N‐terminal deletion mutant of ClC‐2), by patch clamping channels expressed in Xenopus oocytes. 3 With all these channels, reducing [Cl − ] i shifted activation to more negative voltages and reduced the maximal activation at most negative voltages. 4 We also investigated the external halide dependence of WT ClC‐2 using two‐electrode voltage‐clamp recording. Reducing external Cl − ([Cl − ] o ) activated ClC‐2 currents. Replacing [Cl − ] o by the less permeant Br − reduced channel activity and accelerated deactivation. 5 Gating of the ClC‐2 mutant K566Q in normal [Cl − ] o resembled that of WT ClC‐2 in low [Cl − ] o , i.e. channels had a considerable open probability ( P o ) at resting membrane potential. Substituting external Cl − by Br − or I − led to a decrease in P o . 6 The [Cl − ] i dependence of the hyperpolarization‐activated gates of various ClC channels suggests a similar gating mechanism, and raises the possibility that the gating charge for the hyperpolarization‐activated gate is provided by Cl − . 7 The external halide dependence of hyperpolarization‐activated gating of ClC‐2 suggests that it is mediated or modulated by anions as in other ClC channels. In contrast to the depolarization‐activated fast gates of ClC‐0 and ClC‐1, the absence of Cl − favours channel opening. Lysine 556 may be important for the relevant binding site.