Fig. 6. Effects of ketamine (KT; 0.3 and 1 mm) 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 in the endothelium-denuded, fura-2–loaded strips. After recording the control responses to KCl (40 mm), the strips were treated with ketamine for 5 min before and during subsequent cumulative application of various concentrations of Ca²⁺in the presence of 10 μm norepinephrine. In the analyses, the maximal increase in either R^340/380or force induced by KCl before exposure to ketamine was assumed to be 100%, whereas basal values in normal physiologic salt solution were assumed to be 0%. n = 4. KT = ketamine. *P < 0.05 versus  control (100%) within each group. #P < 0.05 versus  control at each Ca²⁺concentration. (C ) Effects of ketamine 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 ketamine was constructed from the data shown in (A ) and (B ).