Fig. 4.

Reduced level or loss of the long dystrophin (Dys)-like product isoforms of Dys results in faster heart rate by shortening the diastolic intervals. (A) Representative M-mode traces (10 s) from high-speed movies of semi-intact flies. Wild-type (wt) flies show rhythmic heart beating at 1-week-old to 3-week-old of age, but moderate arrhythmicity at 5 weeks. dysExel6184/dyskx43 hearts show increased heart rate in 3-week-old and 5-week-old flies. (B) Heart period histograms obtained from 1 min movies plotted as individual data points illustrating the variability of the heart period within a group of flies for controls and dysExel6184/dyskx43 mutants. At 1 week, the mean heart period for wt and dysExel6184/dyskx43 flies is about 0.5 s, which increases in wt to 1 s at 5 weeks. In contrast, aging dysExel6184/dyskx43 shows less of an increase, to only 0.8 s at 5 weeks (bottom panel in B). (C) Standard deviation of the heart period was used as a measure of irregularity in heart rhythm (‘arrhythmicity index’). All time points (except 1 week) show less arrhythmicity for dys mutants compared to wt flies. Differences were estimated by t-test P < 0.05 and are indicated by *. (D) Mean diastolic interval (± SEM) for wt and dys mutant flies obtained from 1 min high-speed movies at the indicated ages. Significant differences were determined by two-tailed independent samples t-test. P values < 0.05 were considered significant (*P < 0.01). (E) Percentage of total flies showing asystoles (prolonged diastolic phases of more than 1 s) in 1-min movie clips. Differences were estimated by t-test P < 0.05 and are indicated by *.