¹ From the Thomas C. Jenkins Department of Biophysics, The Johns Hopkins University, Baltimore, Maryland 21218.

Dr. Mittenthal's present address is Department of Biological Sciences, Stanford University, Stanford, California 94305.

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant . a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation

See PDF for Equation

for temperatures between 1 and 20°C and for sarcomere lengths 2.0–2.8 µm. The energy of activation, E, does not vary significantly with s; E = 13.9 ± 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 µm) is about three times greater than A(2.8 µm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r₀ in a twitch to r for large D. The rate constant for decrease of r with D increases with s and with T. r₀ and r obey the Arrhenius equation and decrease with increasing s.

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