Time course of rise of muscle stiffness at onset of contraction induced by photorelease of ATP.
Isometric contraction (9-10 degrees C) of skinned fibres from rat psoas muscle was elicited by photorelease of ATP (1.3-1.4 mM), and force (F), in-phase (I) and quadrature (Q) stiffness were monitored. The sinusoidal length change for the stiffness measurement was approximately 0.09% fibre length and 200-1000 Hz. On photolysis, F and I initially fell, and then rose. The half-time of the rise of I was shorter than that of F. Contrary to the previous assumption, Q rose even earlier than I. Although the time courses of the rise of F and I were greatly affected by the presence of phosphate ion (Pi; 4 mM), its effect on Q was modest. We propose the following hypothesis: the rigor crossbridges, after binding ATP, initially enter a state characterized by high Q with low I and none or little F, and then, releasing Pi during passing the state with the increased I, reach the final force generating state.
Horiuti
K
K
Department of Physiology, Oita Medical University, Japan.
Sakoda
T
T
Yamada
K
K
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000528:radiation effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004548:Elasticity; D007537:Isometric Contraction; D010710:Phosphates / Q000494:pharmacology; D010782:Photolysis; D016658:Psoas Muscles / Q000502:physiology; D051381:Rats
D010710:Phosphates; C029273:P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D002118:Calcium