Gh. Rossmanith et al., INFLUENCE OF MYOSIN ISOFORMS ON TENSION COST AND CROSSBRIDGE KINETICSIN SKINNED RAT CARDIAC-MUSCLE, Clinical and experimental pharmacology and physiology, 22(6-7), 1995, pp. 423-429
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 degrees C in chemically skinn
ed isometrically contracting cardiac muscles containing V-1 and V-3 is
omyosins. 2. The ATPase activity was measured at various levels of Ca2
+ activation by the enzymatic coupling of ATP hydrolysis with the conv
ersion 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 Ca2+ activ
ation were plotted against the corresponding proportional tensions. Th
e 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 rati
os (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 iso
form 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 o
f crossbridge cycling. It is suggested that the tension economy of V-3
muscle arises principally from an increase in the fraction of time, d
uring the crossbridge cycle, when the crossbridge is exerting force.