Figure 3.

Changes in heart function with age are attenuated in ilk and mys heterozygous mutants. (A) M-mode traces from 10 s movies show heartwall movements in 1-week-old (left) and 5-week-old (right) hearts. Top, w^CS. Middle, ilk^54-wCS/+. Bottom, mys^XG43/+. The incidence of arrhythmia is increased with age in wild-type controls (top panels, see also Ocorr et al., 2007), but 5-week-old ilk^54-wCS/+ hearts (middle right) and mys^XG43/+ hearts (bottom right) present more regular beating patterns than 5-week-old w^CS hearts (top right). (B–E) Plots of physiological parameters of w^CS(●), ilk^54-wCS/+(■), and mys^XG43/+ (▲) at 1, 3, and 5 weeks of age. 20–30 flies were used for each data point. (B) Incidence in heartbeat irregularities indicated by the arrhythmia index (AI) represents the standard deviation of heart period normalized to the median value for each fly (Fink et al., 2009). Arrhythmia index increases with age in wild-type w^CS hearts (P < 0.001 for both 3 and 5 weeks), as previously reported for other wild-type strains (Ocorr et al., 2007). Notably, 5-week ilk^54-wCS/+ and mys^XG43/+ flies had lower AI compared with the age-matched w^CS flies. *P < 0.01, **P < 0.001, two-way ANOVA, see Experimental procedures. (C, D) Diastolic diameter decreases with age in w^CS, and diastolic and systolic diameters decrease mys^XG43/+ flies, but not in ilk^54-wCS/+ flies. *P < 0.01, **P < 0.001, two-way ANOVA. (E) Plots of fractional shortening for w^CS, ilk^54-wCS/+, and mys^XG43/+ flies. 1-week-old mys^XG43/+ flies had a significantly lower fractional shortening compared to w^CS and ilk^54-wCS/+. **P < 0.001, two-way ANOVA. (F) Nanoindentation was performed to determine the stiffness (measured in kiloPascal, kPa) of fly heart tubes at the indicated ages and genotypes. Averages and standard errors are shown along with statistical significance, indicated by a Wilcoxon rank-sum test. Number of flies analyzed per condition is indicated at bottom of each bar. *P < 10⁻⁷. Error bars indicate SEM.