On the contraction of glycerol-extracted muscle fibre bundles under highly isometric conditions.

Abstract

Summary.A new technique for strictly isometric recording of glycerol‐extracted muscle fibre bundles is described. The apparatus works on the principle of a torsion balance.By comparing contractions of fibre bundles of different thickness from rabbit psoas conclusions can be drawn about the diffusion depth for ATP into the bundle. ATP in a concentration of 2.3 × 10‐4 M penetrates about 40 μ into a fibre bundle, probably via the endomysium, the diffusion into a single fibre amounting to only about 1 μ.The final isometric tension is proportional to the circumference of the fibre bundle, not to the cross section area.The magnitude of the final isometric tension and the rate of the isometric contraction have been studied as functions of the ATP concentration.The latency between the moment of immersion of the fibre bundle into the ATP solution and the start of the contraction is compatible with the assumption of an unstirred fluid layer of 30–45 μ around the fibre bundle.Possible factors influencing the course of isometric contraction of glycerol‐extracted muscle fibre bundles are discussed.