Effect of sarcomere length and filament lattice spacing on force development in skinned cardiac and skeletal muscle preparations from the rabbit

Skinned cardiac and skeletal muscle freeze-dried preparations were activated in solutions strongly buffered for Ca2+. The response of single skeletal muscle fibres or thin strips of papillary muscle was investigated in relation to changes in Ca content of the perfusate. Sarcomere length was set and controlled during the experiments. The relation between the negative logarithm of the Ca concentration, the pCa, and the normalized developed force proved to be sigmoidal. The exact position of these curves proved to be dependent upon both sarcomere length and the distance between the filaments. The latter was shown by means of osmotic compression of the fibres using dextran. As a consequence of these observations, it was concluded that the length-tension relation is dependent upon the actual Ca concentration. The results are discussed in terms of cross-bridge interaction.