Fig. 3. Effects of procaine applied with either halothane (HAL, A ) or enflurane (ENF, B ) on responses to consecutively applied each anesthetic and caffeine (20 mm) in the Ca2+-free solution. (A-a ) An example of the effect of procaine on contractions induced by consecutive application of halothane and caffeine in the fura-2–nonloaded strips. Identical results were obtained in the fura-2–loaded strips (not shown). (A-b ) A typical example of the effect of procaine on changes in R340/380induced by consecutive application of halothane and caffeine in the fura-2–loaded strips. The changes in R340/380during application of procaine do not reflect those in the [Ca2+]ibecause of its quenching effect on the fluorescence (see Methods). (B-a, b ) Examples (a ) and the analyzed data (b ; n = 3) on the effects of procaine (applied with enflurane) on contractions induced by the consecutive application of enflurane and caffeine in the fura-2–nonloaded strips. The contractions induced by enflurane (open circles) or caffeine (closed circles) were normalized to a control caffeine-induced contraction (100%; see the uppermost trace of B-a ). CONT = control (no procaine) responses to the consecutive application of enflurane and caffeine. The IC50value for the procaine-induced inhibition of the enflurane contraction was 82.1 μm. * P < 0.05 versus control within each group. (B-c ) An example of the inhibition by procaine of the enflurane-induced increase in R340/380in the fura-2–loaded strips. +/− procaine = in the presence (+, gray) or absence (−, black) of procaine. All arrows indicate the time points when the extracellular Ca2+was removed after the Ca2+load. 0Ca-2G = Ca2+-free, 2-mm EGTA solution.