Ca²⁺ sensitivity of the myofilaments was reduced by OVX.

<p><b>A</b>. Shortening-[Ca²⁺] phase loop plots show that OVX caused a rightward shift in the descending phase of the loop, consistent with a decrease in myofilament Ca²⁺ sensitivity. <b>B</b>. Ca²⁺ levels at 50% relaxation, measured to quantify this shift, were higher in OVX myocytes than in sham controls. <b>C</b>. Myofilament Ca²⁺ sensitivity was lower in OVX hearts, as indicated by a rightward shift in the actomyosin MgATPase activity-[Ca²⁺] curves. <b>D</b>. Maximum actomyosin MgATPase activity was similar in both groups. <b>E</b>,<b>F</b>. OVX increased mean EC₅₀ values compared to sham hearts but had no effect on the Hill coefficient (n=25 sham and 26 OVX myocytes for panel B; n=5 sham and 4 OVX hearts for actomyosin MgATPase assay; *p<0.05; Panel C was analyzed with a two-way ANOVA; main factors of free Ca²⁺ and OVX were significant; other data were analyzed with a t-test; *denotes significant differences).