Figure 1. Changes in tension related to increasing Calcium sup ++ concentration, expressed as pCa (where pCa = -log10[Calcium sup ++]), obtained in a skinned cardiac bundle (top), a skinned type I skeletal fiber (middle), and a skinned type II skeletal fiber (bottom). (A) Changes in tension obtained in control solutions (in the absence of halothane). (B) Changes in tension obtained in the presence of halothane: in cardiac and type I skeletal fibers, 0.75 vol% halothane clearly shifts the threshold of Calcium sup ++ concentration to the right, whereas 2.25 vol% halothane does not exhibit any significant effect in type II skeletal fibers. (C) Changes in tension obtained in control solutions after anesthetic exposure (postanesthetic control). Thirty (cardiac bundles) and twenty (skeletal fibers) minutes elapsed between each experimental condition. Arrows = changes in Calcium sup ++ solutions.