Fig. 4. Myosin light chain (MLC) phosphorylation in response to the stepwise increases in [Ca²⁺]^oin high K⁺(40 mm)–depolarized vascular smooth muscle is shown in the absence or presence of halothane, 0.5 − 4.5%. (A ) Immunoblots showing the two nonphosphorylated MLC isoforms (MLC¹and MLC²) and the two phosphorylated isoforms (MLC¹-P and MLC²-P) after separation by urea–glycerol polyacrylamide gel electrophoresis and visualization by chemiluminescence. As can be seen, the nonphosphorylated isoforms (MLC¹and MLC²) decreased, whereas the phosphorylated isoforms (MLC¹-P and MLC²-P) increased as a function of increasing [Ca²⁺]^o. (B ) Phosphorylation responses in the control (shaded bars), halothane-treated (0.5%, diagonal bars; 2.5%, horizontal bars; 4.5%, open bars), or nifedipine-treated 1 μm, closed bars) vessels are shown. Halothane had no significant effect on MLC phosphorylation, whereas nifedipine significantly inhibited MLC phosphorylation. The percentage MLC phosphorylation was taken as the sum of the densities of the MLC¹-P and MLC²-P bands divided by the total MLC, as described under Materials and Methods. Data are shown as mean ± SD; there are three to six measurements at each data point. **P < 0.01 versus  corresponding control value.