Figure 4. Tracings showing the experimental procedure for studying the effects of halothane on submaximum Ca2+-activated (1 micro Meter) tension development, measurements of fura-2 fluorescence, and myosin light chain isoforms. (A) Time control experiment without halothane. (B) Test experiment with halothane. One micromole per liter Ca2+ was buffered with 7 mM EGTA;+ 0%= 1 micro Meter Ca2++0% halothane;+3% halothane = 1 micro Meter Ca2++3% halothane. The skinned strip was activated by 1 micro Meter Ca2+ until force development reached steady state. The strip was then transferred to a quartz tissue bath, and 150 micro liter of the same solution saturated with various concentrations of halothane (0–3%). The ratio of fura-2 fluorescence was simultaneously recorded within 5 s and at various time intervals thereafter. For quantification of myosin light chain isoforms, the skinned strips were frozen 1 min and 15 min after administration of halothane (open arrows). This figure showed that 3% halothane caused a biphasic response of the skinned strip-an initial increase followed by a decrease in force compared with that of the time control group (+0% halothane, A).