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Am J Physiol Heart Circ Physiol 281: H2133-H2142, 2001;
0363-6135/01 $5.00
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Vol. 281, Issue 5, H2133-H2142, November 2001

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

Yuji Wakayama1, Masahito Miura1, Yoshinao Sugai1, Yutaka Kagaya1, Jun Watanabe1, Henk E. D. J. ter Keurs2, and Kunio Shirato1

1 Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8574, Japan; and 2 Department of Medicine, University of Calgary, Calgary, Alberta T2N4M1, Canada

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 (PeakTPC) and the time between the last stimulus and peak Ca2+ wave (PeakCW) and increased PeakTPC and PeakCW (n = 13) as well as the propagation velocity (Vprop; n = 8). Active force during stretch also increased Vprop (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.

arrhythmias


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