DEFICIT OF THE ISOMETRIC TETANIC TENSION REDEVELOPED AFTER A RELEASE OF FROG-MUSCLE AT A CONSTANT VELOCITY

Frog sartorius muscles tetanized isometrically were released at a constant velocity from lengths lL to lS (Δl = lL - lS; ls >l0). The tension P*S redeveloped after the release was lower than the isometric tension PS at lS, and higher than the isometric tension PL at lL. The tension deficit D is defined as the difference PS-P*S. The timing of the release during the tetanus did not influence D.D/P0 was proportional to Δl/l0. The proportionality constant k was equal to 1.35 ± 0.19 (n = 8) when the velocity of release was 2.5 mm/s. When the muscles were released the same Δl, D was found to be an exponential decreasing function of the velocity. The tension deficit was also found in experiments performed in the region lS < l0. The proportionality constant k was smaller, but the influence of the velocity of the release on D was not modified. When the velocity of the release was changed during the release, D changed accordingly, showing that the effects of Δl and V are multiplicative. These facts suggest a working hypothesis based on the concept that the actin filaments which enter the overlap region during a release are strained by the tetanic stress and therefore unable to make normal cross-bridges. © 1979, Rockefeller University Press., All rights reserved.