Sarcomere length‐tension relations of frog skinned muscle fibres at lengths above the optimum.

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Abstract
Single twitch fibers were dissected from anterior tibial muscles of the frog, R. pipiens, and were then either chemically or mechanically skinned. Short segments of the skinned fibers were transferred to an experimental chamber and mounted between a force transducer and a stationary wire. The average sarcomere length was determined from light photomicrographs of the segments obtained during activation and while relaxed. Activations were maximal, in solutions of pCa 5.49 and at 5.degree. C. Fiber segments having regions in which the striation pattern was highly non-uniform were rejected. The relationship between tension and average sarcomere length was determined for sarcomere lengths between 2.1 and 3.8 .mu.m. Tension always decreased when sarcomere length was increased above .apprx. 2.2 .mu.m. Tension plotted against over-all average sarcomere length lay above data obtained from living fibers. Good agreement with living fibers results was found when tension was plotted against the shortest average sarcomere length within a portion of the segment. Apparently sarcomere length non-uniformities greatly influence the shape of the sarcomere length-tension relation in skinned fibers at long lengths. No evidence was found for a length-dependent influence of Ca on tension development at long lengths during maximal activation.