Inward rectification in ClC-0 chloride channels caused by mutations in several protein regions.
Several cloned ClC-type Cl- channels open and close in a voltage-dependent manner. The Torpedo electric organ Cl- channel, ClC-0, is the best studied member of this gene family. ClC-0 is gated by a fast and a slow gating mechanism of opposite voltage direction. Fast gating is dependent on voltage and on the external and internal Cl- concentration, and it has been proposed that the permeant anion serves as the gating charge in ClC-0 (Pusch, M., U. Ludewig, A. Rehfeldt, and T.J. Jentsch. 1995. Nature (Lond.). 373:527-531). The deactivation at negative voltages of the muscular ClC-1 channel is similar but not identical to ClC-0. Different from the extrinsic voltage dependence suggested for ClC-0, an intrinsic voltage sensor had been proposed to underlie the voltage dependence in ClC-1 (Fahlke, C., R. Rüdel, N. Mitrovic, M. Zhou, and A.L. George. 1995. Neuron. 15:463-472; Fahlke, C., A. Rosenbohm, N. Mitrovic, A.L. George, and R. Rüdel. 1996. Biophys. J. 71:695-706). The gating model for ClC-1 was partially based on the properties of a point-mutation found in recessice myotonia (D136G). Here we investigate the functional effects of mutating the corresponding residue in ClC-0 (D70). Both the corresponding charge neutralization (D70G) and a charge conserving mutation (D70E) led to an inwardly rectifying phenotype resembling that of ClC-1 (D136G). Several other mutations at very different positions in ClC-0 (K165R, H472K, S475T, E482D, T484S, T484Q), however, also led to a similar phenotype. In one of these mutants (T484S) the typical wild-type gating, characterized by a deactivation at negative voltages, can be partially restored by using external perchlorate (ClO4-) solutions. We conclude that gating in ClC-0 and ClC-1 is due to similar mechanisms. The negative charge at position 70 in ClC-0 does not specifically confer the voltage sensitivity in ClC-channels, and there is no need to postulate an intrinsic voltage sensor in ClC-channels.
Ludewig
U
U
Center for Molecular Neurobiology (ZMNH), Hamburg University, D-20246 Hamburg, Germany.
Jentsch
T J
TJ
Pusch
M
M
D000595:Amino Acid Sequence; D000818:Animals; D018118:Chloride Channels / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D004557:Electric Organ / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D010472:Perchlorates / Q000494:pharmacology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D014101:Torpedo / Q000502:physiology*
D018118:Chloride Channels; D010472:Perchlorates