Fig. 3. Effects of intermittent injections of local anesthetic on psoas sarcoplasmic reticulum Ca²⁺content. (  A ) Examples of x–y fluorescence images (  top ) recorded in a control bundles of skinned psoas muscle fibers loaded with Fluo-3 (50 μm) at different times (t1, t2, t3) before and after acute application of 50 μm 4-chloro-  m -cresol. The time course of fluorescence is obtained from the averaged fluorescence measured in region of interest in the fibers (  bottom ) and exhibits a large transient calcium release after application of 4-chloro-  m -cresol reflecting sarcoplasmic reticulum Ca²⁺store. (  B ) This experiment has been performed after intermittent injections of local anesthetic vehicle, bupivacaine, levobupivacaine, and ropivacaine and indicates a lower sarcoplasmic reticulum Ca²⁺store after levobupivacaine treatment. Values are mean ± SD (n = 6/group). *  P < 0.05  versus control group.