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INFLUENCE OF MYOSIN ISOFORMS ON TENSION COST AND CROSSBRIDGE KINETICS IN SKINNED RAT CARDIAC MUSCLE
Author(s) -
Rossmanith G. H.,
Hamilton A. M.,
Hoh J. F. Y.
Publication year - 1995
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1995.tb02034.x
Subject(s) - crossbridge , contractility , chemistry , myosin , atp hydrolysis , biophysics , atpase , cardiac muscle , kinetics , context (archaeology) , muscle contraction , enzyme , biochemistry , anatomy , biology , endocrinology , physics , quantum mechanics , paleontology
SUMMARY 1. In attempting to consolidate the role of ventricular isomyosins in regulating the contractility of the myocardium, actomyosin ATPase and crossbridge kinetics were obtained at 24°C in chemically skinned isometrically contracting cardiac muscles containing V 1 and V 3 isomyosins. 2. The ATPase activity was measured at various levels of Ca 2+ activation by the enzymatic coupling of ATP hydrolysis with the conversion of NADH to NAD + . The crossbridge kinetics were inferred from small‐amplitude perturbations of muscle length and muscle tension, and characterized by the frequency‐domain parameter f min . 3. The ATPase rates of V 1 and V 3 muscles obtained at various levels of Ca 2+ activation were plotted against the corresponding proportional tensions. The ATPase vs tension plots were linear with slopes of 4.92 nmol/min ‐1 per mm per mN and 1.98 nmol/min ‐1 per mm per mN, respectively for, V 1 and V 3 muscles. Individual calculations of ATPase‐to‐tension ratios (nmol/min ‐1 per mm per mN) gave corresponding averages of 4.98 ± 0.12 (s.e.m., n = 12) and 2.16 ± 0.12 (s.e.m., n = 10). The myosin isoform induced proportional change in tension cost was accompanied by a similar change in f min (4.1 ± 0.1 Hz and 1.95 ± 0.03 Hz, means ± s.e.m., for V 1 and V 3 muscles, respectively). 4. The observations and other published kinetic data are discussed in the context of models of crossbridge cycling. It is suggested that the tension economy of V 3 muscle arises principally from an increase in the fraction of time, during the crossbridge cycle, when the crossbridge is exerting force.