Response to Mechanical Stress Is Mediated by the TRPA Channel Painless in the Drosophila Heart
Figure 4
Cardiac response to Painless activation by elevated temperature.
In all cases, semi-dissected preparations were first bathed in the Schneider medium at 25°C (m-modes, left). Then, the temperature of the medium in the perfusion chamber was increased at the indicated values (m-modes, right). (A) M-mode traces from movies recorded after slight temperature increase. The heart rate of wild-type cardiac tube bathed in the medium at 25°C is regular (160 bpm). When the temperature is increased to 36°C, a 14.1% increase in frequency is observed. The same type of response is observed in the pain4 mutant (7.7%) and after transgenic rescue (12.2%). (B) M-mode traces from movies recorded after moderate temperature increase. In the wild-type, the increase of temperature from 25°C to 46°C induces a strong arrhythmia with an important decrease in the cardiac rate (−23.7%). In pain3 individuals, the rise in temperature induces tachycardia (20.2%) but no arrhythmia was observed. The bradycardia and the associated arrhythmia observed in the wild-type are recovered in the pain3 rescue (−18.5%). In both the wild-type and the rescue, the regular beating is progressively recovered when the temperature drops back. (C) M-mode traces from video-movies recorded during high temperature increase. In wild-type, increasing the temperature from 25°C to 50°C leads to a cardiac pause and the heart restarts to beat firstly irregularly, then the basal rhythm is recovered. In the mutant, like for both lower temperatures, increasing the temperature to 50°C induced a strong tachycardia but no cardiac arrest is visible. Rescuing pain expression in the heart restores the cardiac pause and the prolonged arrhythmia. The basal rate is recovered after 12 min.