Fig. 8. Effects of isoflurane on increases in R^340/380(A ) and force (B ) caused by incremental increases in the extracellular Ca²⁺concentration ([Ca²⁺]^e) during stimulation with norepinephrine (0.5 μm) in the fura-2-loaded strips. After the control responses to KCl (40 mm) had been recorded, the strips were treated with isoflurane for 40 min before and during subsequent application of various concentrations of Ca²⁺in the presence of norepinephrine. In these analyses, the maximal increase in either R^340/380or force induced by KCl before exposure to isoflurane was assumed to be 100% and their basal values in normal physiologic salt solution 0%. *P < 0.05 versus  control at each Ca²⁺concentration. n = 4. (C ) Effects of isoflurane on the R^340/380-force relation in the presence of norepinephrine. The R^340/380-force relation either in the absence or in the presence of isoflurane was constructed from the data shown in A  and B . ‡P < 0.05 between the control and isoflurane groups.