Cytoplasmic ATP inhibition of CLC-1 is enhanced by low pH.

The CLC-1 Cl(-) channel is abundantly expressed on the plasma membrane of muscle cells, and the membrane potential of muscle cells is largely controlled by the activity of this Cl(-) channel. Previous studies showed that low intracellular pH increases the overall open probability of recombinant CLC-1 channels in various expression systems. Low intracellular pH, however, is known to inhibit the Cl(-) conductance on the native muscle membrane, contradicting the findings from the recombinant CLC-1 channels in expressed systems. Here we show that in the presence of physiological concentrations of ATP, reduction of the intracellular pH indeed inhibits the expressed CLC-1, mostly by decreasing the open probability of the common gate of the channel.