Figure 5. Relation of cell length to intracellular calcium concentration (as measured by the indo-1 ratio) during individual beats of single rat heart cells. The lower-left corner of each loop represents diastole. During contraction, the trace proceeds first to the right (as intracellular calcium increases) and then upward (as cell shortening occurs). The relaxation phase is the left side of each loop. For each panel, the loop marked “C” represents a beat just before the introduction of anesthetic, and the “T” loop comes from a beat just after the beginning of exposure to anesthetic-containing solution. In A, the anesthetic was 0.69 mM enflurane (1.3 vol%); in B, it was 0.54 mM isoflurane (1.4 vol%); in C, it was 0.40 mM halothane (0.8 vol%). The “T” beats in halothane and enflurane demonstrate the transient increase in twitch, whereas twitch is already decreasing at that same time in isoflurane. The relaxation trajectory of the pairs of beats match for each anesthetic.