Role of connectin in the length-tension relation of skeletal and cardiac muscles.

Resting length-tension relation was studied in glycerinated preparations of frog semitendinosus and atrial muscles. The sarcomere length was measured by using either the light diffraction method or photomicrographs. When the glycerinated preparation was treated with 1 N NaOH solution and subsequently with 2% SDS solution, the resting tension decreased. In glycerinated semitendinosus muscle the resting tension decreased to below 20% of the value before treatment. However, the glycerinated atrial muscle retained more than 50% of its resting tension in spite of such biochemical treatment. The thermoelasticity of the muscle, which was represented by (formula:see text), was determined. Glycerinated semitendinosus and atrial muscles, which were treated with 0.6 M KCl, showed negative beta at all sarcomere lengths. However, when the glycerinated muscle was treated with both alkali (1 N NaOH) and SDS solution, beta at the shorter length became positive (i.e., a rubber-like property). Since connectin survived the biochemical treatment (either NaOH or SDS), it was concluded that the fraction of resting tension, which remained in spite of the biochemical treatments, might be due to the connectin.