β-Adrenergic response. (A, B) Representative single twitches show an increase of force amplitude with increasing isoproterenol concentrations in both groups, but faster in the pH 7.4 group. (C) Relative force amplitudes normalized to baseline force showed a sigmoid shape with increasing isoproterenol. (D) Diastolic tension normalized to baseline revealed no differences between the groups: the tension decreased minimally with increasing isoproterenol. (E) Time to 90% of relaxation was statistically significantly slower in the mild acidotic group than in the control group with pH 7.40. (F) Half-maximal effective concentration (EC50) was statistically significantly different between the pH groups.