1 kgf/cm2--the isometric tension of muscle contraction: implications to cross-bridge and hydraulic mechanisms.

Attention is drawn to experimental results from many laboratories which indicate that the isometric force (F) in the contraction of striated muscle fibers is linearly proportional to their variable cross-section area (A). Reversible swelling of intact, skinned, or glycinerated fibers can be induced by changes in tonicity, ionic strength or pH. In all cases where careful measurements of F and A are reported, the maximal isometric tension namely, T = F/A, is found around 1 kgf /cm2, even though F and A may change more than threefold for a given fiber at a certain length. These results seem to be independent of the fiber length or temperature. Thus, the isometric tension T in striated muscle does not depend on the number or the rate of the interacting cross-bridges. This result of constant isometric tension, which has so far received little attention, is however, a simple prediction of the hydraulic mechanism which is proposed for muscle contraction. Therefore, the hydraulic model, which is based on the hypothesis of vectorial flux of energetic protons deserves serious consideration.