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Original Article

^a From the Department of Physiology, National Yang-Ming University, Taipei, Taiwan 11221
Department of Physiology, National Yang-Ming University, 155, section 2, Li-Nung Street, Taipei, Taiwan, 11221.Fax: 886-2-2826-4049;

tychen{at}ym.edu.tw

The inactivation of the ClC-0 chloride channel is very temperature sensitive and is greatly facilitated by the binding of a zinc ion (Zn²⁺) from the extracellular side, leading to a Zn²⁺-induced current inhibition. To further explore the relation of Zn²⁺ inhibition and the ClC-0 inactivation, we mutated all 12 cysteine amino acids in the channel and assayed the effect of Zn²⁺ on these mutants. With this approach, we found that C212 appears to be important for the sensitivity of the Zn²⁺ inhibition. Upon mutating C212 to serine or alanine, the inactivation of the channel in macroscopic current recordings disappears and the channel does not show detectable inactivation events at the single-channel level. At the same time, the channel's sensitivity to Zn²⁺ inhibition is also greatly reduced. The other two cysteine mutants, C213G and C480S, as well as a previously identified mutant, S123T, also affect the inactivation of the channel to some degree, but the temperature-dependent inactivation process is still present, likewise the high sensitivity of the Zn²⁺ inhibition. These results further support the assertion that the inhibition of Zn²⁺ on ClC-0 is indeed due to an effect on the inactivation of the channel. The absence of inactivation in C212S mutants may provide a better defined system to study the fast gating and the ion permeation of ClC-0.

Key Words: ClC-0 • slow gating • Zn²⁺ inhibition • cysteine mutagenesis

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