External copper inhibits the activity of the large-conductance calcium- and voltage-sensitive potassium channel from skeletal muscle

We have characterized the effect of external copper on the gating properties of the large-conductance calcium- and voltage-sensitive potassium channel from skeletal muscle, incorporated into artificial bilayers. The effect Of Cu2+ was evaluated as changes in the gating kinetic properties of the channel after the addition of this ion. We found that, from concentrations of 20 mum and up, copper induced a concentration-and time-dependent decrease in channel open probability. The inhibition of channel activity by Cu2+ could not be reversed by washing or by addition of the copper chelator, bathocuproinedisulfonic acid. However, channel activity was appreciably restored by the sulfhydryl reducing agent dithiothreitol. The effect of copper was specific since other transition metal divalent cations such as Ni2+, Zn2+ or Cd2+ did not affect BKCa channel activity in the same concentration range. These results suggest that external Cu2+ -induced inhibition of channel activity was due to direct or indirect oxidation of key amino-acid sulfhydryl groups that might have a role in channel gating.