Effect of transient stretch on intracellular Ca2+during triggered propagated contractions in intact trabeculae

Abstract

Transient stretch of cardiac muscle during a twitch contraction may dissociate Ca2+from myofilaments into the cytosol at the moment of quick release of the muscle. We studied the effect of stretch and quick release of trabeculae on changes in intracellular Ca2+([Ca2+]i) during triggered propagated contractions (TPCs). Trabeculae were dissected from the right ventricle of 9 rat hearts. [Ca2+]iwas measured using electrophoretically injected fura-2. Force was measured using a silicon strain gauge and sarcomere length was measured using laser diffraction techniques. Reproducible TPCs (n = 13) were induced by trains of electrical stimuli (378 ± 19 ms interval) for 7.5 s at [Ca2+]oof 2.0 mM (27.9 ± 0.2°C). The latency of the TPC force and the underlying increase in [Ca2+]iwas calculated from the time (TimeF) between the last stimulus and the peak of TPC force (PeakF), or the time (TimeCa) between the last stimulus and the peak of the increase in [Ca2+]iduring the TPCs (PeakCa). As a result of a 10% increase in muscle length for 150-200 ms during the last stimulated twitches, TimeFand TimeCadecreased and PeakFand PeakCaincreased significantly (n = 13). In addition, transient stretch sometimes induced a twitch contraction subsequent to the accelerated TPC and its underlying increase in [Ca2+]i. These results suggest that Ca2+binding and dissociation from the myofilaments by the stretch and quick release of muscle may modulate the TPC force and the underlying increases in [Ca2+]iand play an important role in the induction of arrhythmias.Key words: rat cardiac trabeculae, stretch, calcium transients.