Tension transients in fibrillar muscle fibres as affected by stretch-dependent binding of AMP-PNP: a teinochemical effect?

The recovery in tension after release of a fibrillar muscle preparation as well as the fall in tension after restretch was found to be greater in presence of AMP-PNP than in its absence (rigor). The effect of AMP-PNP was concentration-dependent with an optimum at 0.1 mM corresponding to the dissociation constant of AMP-PNP from the myosin heads. This evidence supports the validity of the teinochemical principle which predicts a stretch-dependent AMP-PNP binding. The stiffness calculated per cross bridge was similar to that found by Huxley and Simmons (1971). It was further calculated that only 15% of the cross bridges are in a force-maintaining state in rigor.