Fig. 6. Effects of halothane on the myosin light chain (MLC) phosphorylation–contraction relationship in high K+–depolarized vascular smooth muscle. As can be seen, halothane (0.5–4.5%) has a clear concentration-dependent inhibitory effect on the phosphorylation–contraction relationship as evidenced by the diminished contractile responses to the increases in MLC phosphorylation. This “MLC phosphorylation” desensitizing effect is similar to the Ca2+desensitizing effect of halothane evident in figure 5Aand likely reflects an effect of halothane on contractile protein activation that is unrelated to MLC phosphorylation (see Discussion). As described in Materials and Methods, the curves shown represent best fits to the Hill equation using the nonlinear least-squares method. Data are shown as mean ± SD; there are three to six measurements per data point.