Heart Muscle Mechanics

Abstract

The goal implicit in the research reviewed above is to describe the contractile behavior of heart muscle in terms of crossbridge and filament behavior. It is necessary to elucidate these details in cardiac muscle because of the distinct biochemical differences between skeletal and cardiac myosin. As is evident in this review, significant advances have been made toward describing unique mechanical properties of cardiac muscle crossbridges. Several major problems now require attention: (a) Activation parameters are labile, making mechanical measurements sensitive to measurement perturbation; (b) significant structural inhomogeneities at the cellular and sarcomere level prevent precise assignment of externally measured force to internal structures (force generators, passive elements) within whole cardiac muscle and individual cells; (c) high resting stiffness and forces of poorly understood origin and properties confound attempts to interpret force measurements and dynamics. The differences between heart and skeletal muscle myosin may provide the means for identifying structural counterparts of the Huxley-Simmons model (33); they may also be useful in evaluating the electrostatic and quantum-mechanical models.

Activation dependence of isotonic transient in response to step tension reduction in cardiac muscle segment during barium contracture

“…Af large amounts of tension reduction, other factors in addition fo this mechanism may be important determinants of transient SL responses, including resting tension produced by parallel elastic elements, infernal resistance, restoring force, deactivation induced by shortening, and motion-dependent inactivation (i.e. 'uncoupling effect'), all of which have been previously reviewed (Alpert et al, 1979). However, these factors, except for the 'uncoupling effect', cannot explain activation-dependent changes in the SL transient response, since they appear fo contribute equally fo the SL transient responses even at different activation levels when the initial SL was fixed fo the saine length (i.e.…”

Energy, structure, conformation, and heart failure

“…Actomyosin complexes formed in the overlapping areas are responsible for generation of a drawing force and relative sliding of thin and thick filaments without changing their length, i.e. contraction, In canine myocardium, the end-diastolic length of a sarcomere in the left ventricle varies from 2.07 [42] to 2.25 g [20], while by the end of systole it decreased to 1.8-1.9 ~ [20] (during normal contraction, shortening by 12%) or to 1.6 ~ [42,89] (hypercontraction, shortening by 25%).…”

Mechanical properties of gastrointestinal smooth muscle

“…If care is taken to recognize both the power and limitations of such extrapolations, much understanding can be gained. There are many extensive reviews of this literature (3, 8,108,151); in this chapter concepts that are necessary to the discussion are introduced when appropriate. This may result in an incomplete treatment of some areas of the subject, but the reviews cited can be used to fill in the inevitable gaps.…”