Keisuke Horiuti

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ATP (1–1.2mm) was photoreleased from caged ATP (5mm) in skinned fibres from rat psoas muscle at 15–17° 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(More)
The mechanism of the inhibitory effect of 2, 3-butanedione 2-monoxime (BDM) on contraction of frog skeletal muscles was studied using skinned fibres and aequorin-injected intact fibres. The tension development of skinned fibres directly activated with calcium was strongly inhibited by BDM. This agent also had effects on the sarcoplasmic reticulum in the(More)
1. The cross-bridges in slow- and fast-twitch fibres (taken, respectively, from soleus and psoas muscles of rats) were examined in mechanical experiments using caged ATP and X-ray diffraction, to compare their binding of ATP and ADP. 2. Caged ATP was photolysed in rigor fibres. When ADP was removed from pre-photolysis fibres, the initial relaxation (+/-(More)
To induce isometric contraction in the absence of Ca2+ (10mm EGTA), low concentrations (130 μM) of ATP were photoreleased from caged ATP in skinned fibres from rat psoas muscle at 15–16° C. The magnitude of contraction was independent of the concentration of EGTA (1–30mm). Each isometric transient (i) was paired with another (s) obtained under the same(More)
We isometrically activated skinned fibers in rigor by flash photolysis of caged ATP at various [Ca2+] at 8 degrees C. On release of ATP, tension initially decreased with the same time course at all [Ca2+]. At high [Ca2+] (pCa < or = 5.8), tension rose to the steady-state plateau after the brief relaxation. When the [Ca2+] was intermediate (7.0 < or = pCa <(More)
1) We photoreleased ATP in skinned muscle fibers from rat psoas, and examined the effects of ADP on the ATP-induced isometric transient. 2) On release of ATP, the muscle stiffness initially falls at any [Ca2+]. ADP slowed this stiffness decrease, suggesting competition between ADP and ATP. Even in the presence of ADP, the rate of stiffness decrease was(More)
Effects of ADP on the conformation of myosin cross-bridges were studied in x-ray diffraction experiments on single skinned fibers of frog skeletal muscle by photorelease of ADP from caged-ADP. The experiments were performed at the third-generation synchrotron radiation facility SPring-8 with a time resolution of 5 ms. The intensity of the third-order(More)
X-ray diffraction experiments were performed on rat soleus and psoas muscles using synchrotron radiation from a multipole wiggler. The X-ray diffraction patterns were recorded at a time resolution of 16.7 ms with an X-ray image intensifier and a CCD video camera. A bundle of 10-15 muscle fibres was activated by photorelease of 2.2 mM ATP from 7 mM caged-ATP(More)
Effects of 20 mM inorganic phosphate on the cross-bridge behavior after photorelease of ATP from caged ATP was studied by X-ray diffraction in rat skinned psoas muscle fibers at 16°C. In the first 30 ms after the photorelease, tension was similar in the presence and absence of phosphate. The tension development was then suppressed in the presence of(More)
Flash photolysis of caged ATP was first employed in muscle cell physiology about 15 years ago. This technique enables examination of the millisecond dynamics of synchronized cross-bridge ATPases in muscle fibers, and consequently, many photolysis studies have been performed in attempt to elucidate the cross-bridge mechanism. The results of early studies(More)