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The voltage‐dependent ClC‐2 chloride channel has a dual gating mechanism
Author(s) -
Zúñiga Leandro,
Niemeyer María Isabel,
Varela Diego,
Catalán Marcelo,
Cid L. Pablo,
Sepúlveda Francisco V.
Publication year - 2004
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.2003.060046
Subject(s) - gating , chloride channel , chemistry , mechanism (biology) , biophysics , dual (grammatical number) , channel (broadcasting) , computer science , biochemistry , physics , biology , telecommunications , quantum mechanics , art , literature
Functional and structural studies demonstrate that Cl − channels of the ClC family have a dimeric double‐barrelled structure, with each monomer contributing an identical pore. Single protopore gating is a fast process dependent on Cl − interaction within the selectivity filter and in ClC‐0 has a low temperature coefficient over a 10°C range ( Q 10 ). A slow gating process closes both protopores simultaneously, has a high Q 10 , is facilitated by extracellular Zn 2+ and Cd 2+ and is abolished or markedly reduced by mutation of a cysteine conserved in ClC‐0, ‐1 and ‐2. In order to test the hypothesis that similar slow and fast gates exist in the widely expressed ClC‐2 Cl − channel we have investigated the effects of these manoeuvres on ClC‐2. We find that the time constants of both components of the double‐exponential hyperpolarization‐dependent activation (and deactivation) processes have a high temperature dependence, with Q 10 values of about 4–5, suggesting important conformational changes of the channel. Mutating C256 (equivalent to C212 in ClC‐0) to A, led to a significant fraction of constitutively open channels at all potentials. Activation time constants were not affected but deactivation was slower and significantly less temperature dependent in the C256A mutant. Extracellular Cd 2+ , that inhibits wild‐type (WT) channels almost fully, inhibited C256A only by 50%. In the WT, the time constants for opening were not affected by Cd 2+ but deactivation at positive potentials was accelerated by Cd 2+ . This effect was absent in the C256A mutant. The effect of intracellular Cl − on channel activation was unchanged in the C256A mutant. Collectively our results strongly support the hypothesis that ClC‐2 possesses a common gate and that part of the current increase induced by hyperpolarization represents an opening of the common gate. In contrast to the gating in ClC‐0, the protopore gate and the common gate of ClC‐2 do not appear to be independent.