title: Stretch and quick release of rat cardiac trabeculae accelerates Ca2+ waves and triggered propagated contractions.
abstract: 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 degrees 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 microM 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.
authors.affiliation: Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8574, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Wakayama
authors.forename: M
authors.initials: M
authors.lastname: Miura
authors.forename: Y
authors.initials: Y
authors.lastname: Sugai
authors.forename: Y
authors.initials: Y
authors.lastname: Kagaya
authors.forename: J
authors.initials: J
authors.lastname: Watanabe
authors.forename: H E
authors.initials: HE
authors.lastname: ter Keurs
authors.forename: K
authors.initials: K
authors.lastname: Shirato
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005682:Gadolinium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005682:Gadolinium; D002118:Calcium