Fig. 4. (A ) The apparent rate of desensitization is plotted as a function of acetylcholine concentration in the absence of isoflurane (filled circles) and in the presence of 1.0 mM isoflurane (open circles) from reference 12. The dotted curve is a fit of the control data (no isoflurane) to assuming a value of 0.039 for K  ^o. 19Because only channel-opening concentrations of acetylcholine were used in that study, the values for K  ^Band K  ^des3were taken from table 2using another preparation. The completely overlapping solid and dashed curves demonstrate the effect of reducing either K  ^d2or K  ^oby 12-fold. (B ) The apparent rate of desensitization versus  suberyldicholine concentration determined using is plotted. The dotted curve is derived from the kinetic constants in table 2(for suberyldicholine) in the absence of isoflurane, whereas the solid and dashed curves demonstrate the effect of reducing either K  ^d2or K  ^oby 12-fold.