Studies on the origin of resting tension of skeletal muscle

Glycerol extracted frog skeletal muscle fibres at 2.2 μm sarcomere length (in situ-length) in a solution free of Ca⁺⁺ and Mg⁺⁺ but containing ATP, show a decrease in both their resting tension and their elastic modulus, if the ionic strength of the bathing solution is increased. This finding is compared with the behaviour of intact skeletal muscle fibres in hypertonic solution. It is concluded that the resting tension of intact skeletal muscle fibres at in situ-length is caused by the longitudinal sarcoplasmic reticulum as well as by interactions between the contractile filaments.