Effects of gender on the sensitivity of rat cardiac muscle to extracellular Ca2

Experiments were designed to determine if the inotropic response to increasing buffer calcium concentration differs in male and female cardiac muscle. Left atrial and papillary muscles were isolated from hearts of 3-4-month old male and female rats, bathed in Krebs-Henseleit solution (30 degrees C), and stimulated at 1.5 Hz. Isometric developed tension was monitored continuously as extracellular Ca2+ was increased in a cumulative fashion. When compared to male atrial muscle, female atrial preparations were more sensitive to the resulting positive inotropic action; EC50 values were 2.89 +/- 0.22 and 1.86 +/- 0.21 mM in male and female atria, respectively. Two-way analysis of variance (ANOVA) also indicated that there was a significant gender-associated difference in the Ca2+ dose-response curves in atrial muscle. In contrast, papillary muscle did not show a significant gender-related difference in EC50 values (0.88 +/- 0.07 and 0.74 +/- 0.06 mM in males and females); however, the Ca2+ dose-response curves obtained from male and female preparations were found to be significantly different when compared by ANOVA.