Evidence for cross-bridge attachment in relaxed muscle at low ionic strength.

AUTOR(ES)

Brenner, B

RESUMO

In vitro at low ionic strength (mu = 0.02 M) and 5 degrees C, myosin subfragment-1 shows significant binding to regulated actin in the presence of ATP, independent of the concentration of free Ca2+. Under the same conditions, single skinned rabbit psoas muscle fibers develop force only in the presence of Ca2+ and are relaxed in its absence. However, the stiffness, measured with very rapid stretches (0.5% of muscle length in 0.1 ms), is high even when the fibers are relaxed. This "rapid stiffness" of the resting muscle is sensitive to ionic strength, becoming small at normal ionic strength (mu = 0.17 M). At low ionic strength, the rapid stiffness is approximately proportional to the overlap between the actin and myosin filaments. At zero overlap (sarcomere length = 3.8 microns), the stiffness is less than 20% of the value measured at full overlap. This remaining 20% is relatively insensitive to ionic strength, like the passive resting tension, and it may in fact be due to the structures responsible for the resting tension. Thus, both in vitro binding and the effect of overlap on rapid stiffness measurements in fibers suggest that cross-bridges are attached to actin in relaxed muscle at low ionic strength.

Documentos Relacionados

• Cross-bridge behaviour in skinned smooth muscle of the guinea-pig taenia coli at altered ionic strength.
• Evidence for cross-bridge order in contraction of glycerinated skeletal muscle.
• Cross-bridge scheme and force per cross-bridge state in skinned rabbit psoas muscle fibers.
• Strain-dependent cross-bridge cycle for muscle.
• Evidence for increased low force cross-bridge population in shortening skinned skeletal muscle fibers: implications for actomyosin kinetics.