title: Kinetics of cardiac muscle contraction and relaxation are linked and determined by properties of the cardiac sarcomere.
abstract: The regulation of myocardial contraction and relaxation kinetics is currently incompletely understood. When the amplitude of contraction is increased via the Frank-Starling mechanism, the kinetics of the contraction slow down, but when the amplitude of contraction is increased with either an increase in heart rate or via β-adrenergic stimulation, the kinetics speed up. It is also unknown how physiological mechanisms affect the kinetics of contraction versus those of relaxation. We investigated contraction-relaxation coupling in isolated trabeculae from the mouse and rat and stimulated them to contract at various temperatures, frequencies, preloads, and in the absence and presence of β-adrenergic stimulation. In each muscle at least 16 different conditions were assessed, and the correlation coefficient of the speed of contraction and relaxation was very close (generally >0.98). Moreover, in all but one of the analyzed murine strains, the ratio of the minimum rate of the derivative of force development (dF/dt) over maximum dF/dt was not significantly different. Only in trabeculae isolated from myosin-binding protein-C mutant mice was this ratio significantly lower (0.61 ± 0.07 vs. 0.84 ± 0.02 in 11 other strains of mice). Within each strain, this ratio was unaffected by modulation of length, frequency, or β-adrenergic stimulation. Rat trabeculae showed identical results; the balance between kinetics of contraction and relaxation was generally constant (0.85 ± 0.04). Because of the great variety in underlying excitation-contraction coupling in the assessed strains, we concluded that contraction-relation coupling is a property residing in the cardiac sarcomere.
authors.affiliation: Department of Physiology and Cell Biology and D. Davis Heart Lung Institute, College of Medicine, The Ohio State University, Columbus, OH 43210-1218, USA. janssen.10@osu.edu
authors.forename: Paul M L
authors.initials: PM
authors.lastname: Janssen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D020013:Calcium Signaling / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D023421:Models, Animal; D009126:Muscle Relaxation / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D011486:Protein C / Q000502:physiology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012518:Sarcomeres / Q000502:physiology*; D013696:Temperature; D013997:Time Factors
chemical_list: D011486:Protein C; D011943:Receptors, Adrenergic, beta