Stretch and quick release of rat cardiac trabeculae accelerates Ca²⁺ waves and triggered propa gated 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°C 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 μM 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 Pea_kCW (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.