Effects of ethylene glycol on the kinetics of contraction on flash photolysis of caged ATP in rat psoas muscle fibres.
ATP (1-1.2 mM) was photoreleased from caged ATP (5 mM) in skinned fibres from rat psoas muscle at 15-17 degrees C, to examine the effects of ethylene glycol (EG; 20% in solvent) on the kinetics of isometric contraction. Muscle fibres were stretched by 0.5-2% before photolysis, so that force just before photolysis was almost equal to the steady-state force after photolysis. At the phase of steady-state contraction, force and 500 Hz-stiffness in the presence of EG were 50% and 70% of the controls, respectively, resulting in a higher stiffness-to-force with EG, as reported previously. Following photolysis, force fell before rising to a steady-state plateau. The estimated rate constant of the force decay was approximately 90 s-1, and in the presence of EG was 80-85% of the control. This suggested a small effect of EG on the crossbridge detachment induced by ATP. The rate of force redevelopment was approximately 70 s-1, and EG decreased this rate to 50% of the control. This suggested that EG greatly slows the transition of the crossbridges from the detached state to the reattached force-producing state. The time course of the stiffness signals was consistent with this interpretation. The high stiffness-to-force ratio with EG indicated that EG not only reduces the rate constants which were directly examined in this study but also modifies other aspects of the crossbridge reaction.
Horiuti
K
K
Department of Physiology, Medical College of Oita, Japan.
Sakoda
T
T
Takei
M
M
Yamada
K
K
D000255:Adenosine Triphosphate / Q000528:radiation effects*; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D003198:Computer Simulation; D019855:Ethylene Glycol; D005026:Ethylene Glycols / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D017830:Octoxynol; D010782:Photolysis; D011092:Polyethylene Glycols / Q000494:pharmacology; D016658:Psoas Muscles / Q000187:drug effects; D051381:Rats; D014466:Ultraviolet Rays
D005026:Ethylene Glycols; D011092:Polyethylene Glycols; D000255:Adenosine Triphosphate; D017830:Octoxynol; D019855:Ethylene Glycol