The decrease in P_o of Cx50 hemichannels caused by BQ⁺ is concentration dependent and is a result of an increase in loop gating. Recordings of single Cx50 hemichannels before and after the addition of 300 µM, 500 µM, and 1 mM BQ⁺ applied to the extracellular face. 15-s segments of current traces recorded at a membrane potential of −70 mV along with corresponding all-points histograms obtained from longer (30-s) recordings (right of each trace) are shown. In the absence of BQ⁺, Cx50 hemichannels are predominantly open (O) at −70 mV, with occasional brief transitions to the fully closed state (C). The application of BQ⁺ caused a reduction in the P_o, evident as an increase in the frequency of transitions to the fully closed state. Views of the current traces recorded with or without BQ⁺ at an expanded time scale. The boxed regions indicate the segments of the traces that were expanded. In the presence of BQ⁺, the transitions between open and closed states exhibit slow kinetics, indistinguishable from intrinsic gating events (see control trace) attributed to loop gating. Asterisks show more stable closing events in 1 mM BQ⁺.