The mechanical properties, as revealed by minute length changes, of isolated twitch fibers of the frog have been studied at rest and during low-level activation. Resting tension is 77 ± 23 mN/cm2 (mean ± SD) at 2.2 µm sarcomere length.1 The slope of the tension curve (ΔP/ΔL) recorded during a constant-speed length change of a resting fiber is initially large. At length changes exceeding about 0.18 % of the initial length of the fiber ΔP/ΔL falls abruptly and remains close to zero during the rest of the length change. The amplitude of the tension response is reduced after a length change and returns to normal in about 3 min. Hypertonic sucrose-Ringer solutions cause a small, maintained rise in tension up to 1.4–1.6 times normal osmotic strength. Higher sucrose concentrations cause relatively large, transient tension responses. The initial ΔP/ΔL is increased in moderately hypertonic solutions; it may be reduced in more strongly hypertonic solutions. Elevated [K]o (range 10–17.5 mM) causes a marked reduction in ΔP/ΔL. In this range of [K]o the reduction is not accompanied by changes in resting tension. Addition of 1–1.5 mM caffeine to the Ringer solution affects the resting tension very little but also reduces ΔP/ΔL. The results suggest that stiffness and tension development are not related in a simple way.
Article|
August 01 1971
The Effect of Low-Level Activation on the Mechanical Properties of Isolated Frog Muscle Fibers
J. Lännergren
J. Lännergren
From the Nobel Institute for Neurophysiology, Karolinska Institutet, S-104 01 Stockholm 60, Sweden
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J. Lännergren
From the Nobel Institute for Neurophysiology, Karolinska Institutet, S-104 01 Stockholm 60, Sweden
Received:
March 16 1971
Online ISSN: 1540-7748
Print ISSN: 0022-1295
Copyright © 1971 by The Rockefeller University Press
1971
J Gen Physiol (1971) 58 (2): 145–162.
Article history
Received:
March 16 1971
Citation
J. Lännergren; The Effect of Low-Level Activation on the Mechanical Properties of Isolated Frog Muscle Fibers . J Gen Physiol 1 August 1971; 58 (2): 145–162. doi: https://doi.org/10.1085/jgp.58.2.145
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