Figure 4. Concentration-dependent effect of halothane on single-channel currents. (A) Representative records before and during perfusion of a cell-attached patch on a pleural sensory neuron with the indicated concentrations of halothane. The recording pipette contained ASW and 10 mM tetraethylammonium. V^hwas +20 mV. Large-amplitude openings became more frequent in the presence of halothane, whereas small-amplitude openings were rare. Both types of channel activity returned toward control levels after wash. (B) Concentration-dependent actions of halothane are shown. Mean open probability (NP^o) measures were obtained from experiments in which halothane was delivered to cell-attached patches on pleural sensory neurons. The recording pipettes contained ASW and 10 mM tetraethylammonium. V^hwas +20 mV. NP^oincreased in proportion to the concentration of halothane. The smooth curve was drawn with Equation 1and was best fit with a Hill coefficient (N) of approximately 6 and K = approximately 500 micro Meter. Error bars represent SEM. Mean open probability values were normalized to the average mean open probability for 2 or 3 min of continuous data immediately before halothane perfusion.