Substrate-concentration dependence of contraction parameters in glycerinated insect flight muscle fibers from Lethocerus derollei.

The contraction characteristics of the dorsal longitudinal muscle of Lethocerus derollei were investigated by applying small sinusoidal length changes (+/- 1% of resting length) to glycerinated muscle bundles and studying the effect of varying the frequency from 0.1 to 10 Hz and the concentration of MgATP from 35 microM to 2.3 mM. The maximum work done by the muscle per cycle increased as the MgATP concentration was decreased from 2.3 mM to 52 microM. Between 52 and 35 microM, the maximum work suddenly changed from a positive to a negative value. The optimal frequency for maximal work shifted from low to high values with increase in the MgATP concentration. As the temperature was increased, the optimal work frequency in 2.3 mM MgATP solution shifted to a higher value. As the MgATP concentration was increased, the optimal frequency for maximal power increased. The maximal value of the power was an increasing function of the MgATP concentration, reaching a plateau above 52 microM MgATP. The muscle stiffness was a decreasing function of the MgATP concentration, and above 52 microM MgATP it reached a minimum of about 22% of that in the rigor solution. These results are discussed in relation to the crossbridge kinetics.