Temperature dependence of human muscle ClC-1 chloride channel

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 Q(10) values of similar to3 and similar to4, respectively. Current amplitude increased with increasing temperature with a Q(10) of similar to1.6. 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 similar to 23 and similar to 34 mV per 10 degreesC increase in temperature, for the fast and slow gate, respectively. 4. At low pH, thc 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 Q(10) of gating relaxations at negative potentials of similar to5. The Arrhenius plot of ClC-1 conductance at low pH had a clear break point at similar to 25 degreesC, with higher Q(10) 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.