Stretch and quick release of rat cardiac trabeculae accelerates Ca2+ waves and triggered propagated contractions

Rapid shortening of active cardiac muscle [quick release (QR)] dissociates Ca2+ from myofilaments. We studied, using muscle stretches and QR, whether Ca2+ dissociation affects triggered propagated contractions (TPCs) and Ca2+ waves. The intracellular Ca2+ concentration was measured by a SIT camera in right ventricular trabeculae dissected from rat hearts loaded with fura 2 salt, force was measured by a silicon strain gauge, and sarcomere length was measured by laser diffraction while a servomotor controlled muscle length. TPCs (n=27) were induced at 28 degreesC by stimulus trains (7.5 s at 2.65 +/-0.13 Hz) at an extracellular Ca2+ concentration ([Ca2+](o)) = 2.0 mM or with 10 muM Gd3+ at [Ca2+](o) = 5.2 +/-0.73 mM. QR during twitch relaxation after a 10% stretch for 100-200 ms reduced both the time between the last stimulus and the peak TPC (Peak(TPC)) and the time between the last stimulus and peak Ca2+ wave (Peak(CW)) and increased Peak(TPC) and Peak(CW) (n=13) as well as the propagation velocity (V-prop; n=8). Active force during stretch also increased V-prop (r=0.84, n=12, P<0.01), but Gd3+ had no effect (n=5). These results suggest that Ca2+ dissociation by QR during relaxation accelerates the initiation and propagation of Ca2+ waves.