Fig. 7. Effect of bupivacaine (10 and 100 μm) on Ca²⁺-independent active tension. Results are shown in pMg-adenosine triphosphate (pMgATP)–tension relations. Tension was normalized with respect to maximal tension at pMgATP 5.5, 5.5, and 5.63, respectively, in the absence (control) and presence of 10 and 100 μm bupivacaine. Data obtained for each preparation was fitted to the Hill equation with the mean values of pMgATP⁵⁰and n^H. Absolute values of maximal tension were 25.24 ± 3.61, 20.56 ± 3.37, and 15.09 ± 2.89 kN/m², respectively, in the absence (control) and presence of 10 and 100 μm bupivacaine, and the values were significantly different as follows: 10 μm versus  control (P < 0.05), 100 μm versus  control (P < 0.01), and 100 μm versus  10 μm (P < 0.05). Data obtained for each preparation were fitted to the Hill equation with the mean values of pMgATP⁵⁰and n^H. Vertical bars are SEM of five data points.