Fig. 5. Comparison of the response to dantrolene (100 μm;A ) and ryanodine (0.3 μm;B ) expressed as percent of baseline active force (AF) during postnatal maturation. d3 = 3-day-old rats; d10 = 10-day-old rats; d17 = 17-day-old rats. These concentrations induced comparable negative inotropic effect in the adult rat. Developmental changes in the pharmacologic response to dantrolene were more rapid than those of ryanodine. Data are mean ± SD. * P < 0.05 versus adult.