Tension development and sarcomere length in rat cardiac trabeculae. Evidence of length-dependent activation.

Abstract

SUMMARY We studied the influence of inotropic factors on the shape of the relation between tension and sarcomere length. Tension measurements were performed on thin trabeculae dissected from the right ventricle of the rat heart. Sarcomere length was measured by laser diffraction techniques and controlled by a servomotor system. The relations between tension and sarcomere length were derived from contractions at various extracellular calcium concentrations [Ca 2+ ] o . The time course of tension development was dependent on both sarcomere length and [Ca 2+ ] o . At all [Ca 2+ ] o , the tension attained during contraction was zero at sarcomere lengths of 1.55-1.60 pm and maximal at a sarcomere length of 2.35 /im. Neither a summit nor a descending limb was found in the sarcomere length-tension relation. At [Ca 2+ ] o = 0.5 mM, tension increased linearly with sarcomere length, whereas at [Ca 2+ ] o = 2.5 mM, it approached maximal tension exponentially with sarcomere length. The relations between tension and sarcomere length derived from isometric contractions of the muscle and of sarcomeres were identical, and this suggests that shortening of sarcomeres does not contribute significantly to the effect of [Ca 2+ ] o . The relations between tension and sarcomere length obtained at [Ca 2+ ] o = 0.5 mM from contractions 30 seconds after a potentiating burst of stimuli (4 seconds at 4 Hz) were identical to the relation between tension and sarcomere length at [Ca 2+ ] o = 2.5 mm. Our results are consistent with the hypothesis that cardiac muscle length affects contractile performance by its influence on excitation contraction coupling. CircRes 46: [703][704][705][706][707][708][709][710][711][712][713][714] 1980 THE shape of the relation between tension and sarcomere length in cardiac papillary muscle suggests length-dependent activation of the contractile system (Jewell, 1977). However, there are no data on the effect of inotropic interventions on this curve. Only muscle length-tension curves are available, and these give conflicting results (Jewell, 1977;Huntsman and Stewart, 1977;Sonnenblick, 1962;Bodem et al., 1976). It is known that during isometric contractions there is considerable shortening of sarcomeres in the central region of papillary muscle. This happens at the expense of stretch of damaged regions near the clamps holding the ends of the specimen (Krueger and Pollack, 1975;Pollack and Krueger, 1976;Julian et al., 1976;Julian and Sollins, 1975). The damaged regions as well as the normal region may be influenced by inotropic factors. The interpretation of results of isometric contractions of the muscle is therefore ambiguous. The purpose of the present study was to examine the effect of different calcium concentrations on the relations Supported by Grants 74022 and 77086 from the Netherlands Heart Foundation.Dr. ter Keurs is an Established Investigator of the Netherlands Heart Foundation.Address for reprints: Henk E.D.J. ter Keurs, Department of Cardiology, Medical Faculty, State Un...

Frank-Starling law of the heart and the cellular mechanisms of length-dependent activation

“…However, the relationship between contractile force and sarcomere length is far too steep and to variable between contractile states (Fig. 1B) to be solely explained by such a simple mechanism [1,20,21].…”

“…Furthermore, the shape of the relationship is modulated by contractile state such that more force is generated at a given sarcomere length when contractile activation is elevated (illustrated in Fig. 1B) [21]. What cellular mechanisms might underlie this phenomenon?…”

“…Indeed, twitch force in isolated cardiac muscle has been shown to be directly proportional to systolic sarcomere length [21]. Furthermore, the shape of the relationship is modulated by contractile state such that more force is generated at a given sarcomere length when contractile activation is elevated (illustrated in Fig.…”

“…B Schematic illustration of the relationship between peak twitch force and systolic sarcomere length in isolated cardiac muscle. An increase in contractile state, in this case increased concentration of Ca 2+ in the bathing medium, results both in an elevation of the peak twitch force-sarcomere length relationship as well as a change in the shape of this relationship: for a given end-systolic sarcomere length, peak twitch force is increased [20,21]. C Schematic illustration of the relationship between activator calcium concentration and myofilament force generation [7,17,20].…”

Feasibility and Accuracy of Cardiac Magnetic Resonance Imaging–Based Whole‐Heart Inverse Potential Mapping of Sinus Rhythm and Idiopathic Ventricular Foci

“…These include image misregistration due to patient respiration, inaccurate cardiac geometry due to image acquisition during different phases of the cardiac cycle, and substantial regional variations in cardiac displacement during contraction and relaxation (ranging between 5 and 25 mm) 17, 18. In particular, the base of the heart moves ≥20 mm toward the apex.…”