Fig. 6. Effects of halothane (HAL), enflurane (ENF), isoflurane (ISO), and sevoflurane (SEV) on the norepinephrine-induced increases in R^340/380and force in the Ca²⁺-free solution (n = 4 or 5). (A ) Examples: the responses in either presence (+) or absence (−) of each anesthetic were depicted with gray and black lines, respectively. 0Ca-2G = Ca²⁺-free, 2-mm EGTA solution. Arrows indicate the peaks of responses. (B  and C ) Concentration–response data for the anesthetic-induced increases in R^340/380and force (B ) and the norepinephrine-induced increases in R^340/380and force in the presence of each anesthetic (C ). The increases in R^340/380and force induced by each anesthetic or caffeine were normalized to the control norepinephrine-induced increases in R^340/380and force, respectively. * P < 0.05 versus  control within each group. #P < 0.05 between halothane and enflurane groups at each concentration.