Effects of 2,3-butanedione monoxime on the crossbridge kinetics in frog single muscle fibres.
The effects of 2,3-butanedione monoxime (BDM) on contraction characteristics were studied at 5 degrees C in single intact fibres isolated from the tibialis anterior muscle of the frog. The force-velocity relation was determined using the controlled-velocity method in either whole fibres or short fibre segments in which sarcomere shortening was measured by a laser light diffraction method. It is shown that 3 mM BDM decreases the speed of rise and the amount of tetanus tension, reduces the maximum velocity of shortening and increases the curvature of the force-velocity relation, as well as the value for the stiffness to tension ratio. BDM also slowed down the redevelopment of tetanus tension after a period of unloaded shortening both in fixed-end and in length-clamp conditions. In normal and in BDM-treated fibres length-clamping increased the speed of the initial rise of tetanus tension but not that of the recovery after shortening. The observed force-velocity data points were fitted by the Huxley (1957) equation. It was found that BDM produces a conspicuous decrease of the rate constant for crossbridge attachment. This effect, and also a reduction of the force per crossbridge, are responsible for the depression of the contractile characteristics produced by BDM.
Bagni
M A
MA
Dipartimento di Scienze Fisiologiche, Università di Firenze, Italy.
Cecchi
G
G
Colomo
F
F
Garzella
P
P
D000205:Actomyosin / Q000187:drug effects*; D000818:Animals; D001696:Biomechanical Phenomena; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D011893:Rana esculenta
C004717:diacetylmonoxime; D000205:Actomyosin; D003931:Diacetyl