Fig. 6. Effects of ryanodine (Ryn; 10 µmol l^-1) in immature male (A) and female (B) cardiac tissue. Ventricle strips were incubated with Ryn 15 min prior to the addition of either increased Ca²⁺ (5 mmol l^-1), testosterone (T; 0.3 µmol l^-1), 17ß-estradiol (E2; 1 nmol l^-1) or epinephrine (Epi; 1 µmol l^-1). Plus (+) and minus (-) denote presence and absence, respectively, of specific compounds in the incubation medium. For immature males and females, elevated Ca²⁺ or Epi, but not sex steroids, increased twitch force when glucose (5 mmol l^-1) was present. ^*P<0.05. Values are means ± s.e.m. (N=6-8 strips per group).