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Temperature dependence of human muscle ClC-1 chloride channel

B. Bennetts *, M. L. Roberts *, A. H. Bretag *† and G. Y. Rychkov *†

1. In the present work we investigated the dependence on temperature of the ionic conductance and gating of human muscle ClC-1 chloride channels, transiently expressed in human embryonic kidney (HEK 293) cells.
2. At normal pH, ClC-1 currents deactivated at negative potentials with a double-exponential time course. The time constants of the exponential components, corresponding to the relaxations of the fast and slow gates, were temperature dependent with Q₁₀ values of ~3 and ~4, respectively. Current amplitude increased with increasing temperature with a Q₁₀ of ~1.6.
3. The voltage dependence of the two gating processes was shifted towards more positive potentials with increasing temperature. The half-saturation voltage (V_1/2) of the steady-state open probability (P_o) was shifted by ~23 and ~34 mV per 10 °C increase in temperature, for the fast and slow gate, respectively.
4. At low pH, the voltage dependence of ClC-1 was reversed and currents were activated by hyperpolarisation with a single-exponential time course. This type of gating in ClC-1 resembled the slow gating of the Torpedo ClC-0 homologue, but differed with respect to its kinetics and temperature dependence, with a Q₁₀ of gating relaxations at negative potentials of ~5. The Arrhenius plot of ClC-1 conductance at low pH had a clear break point at ~25 °C, with higher Q₁₀ values at lower temperatures.
5. The temperature sensitivity of relaxation and open probability of the slow gate, which in both ClC-0 and ClC-1 controls two pores simultaneously, implies that the slow gating of ClC-1 is mechanistically different from that of ClC-0.

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