Contractile activation was studied in frog single muscle fibers treated with tetrodotoxin to block action potentials. The membrane potential in a short segment of the fiber was controlled with a two-electrode voltage clamp, and the contractile response of superficial myofibrils in this segment was observed microscopically. The strength-duration relation for contractile activation was similar to that reported by Adrian, Chandler, and Hodgkin (1969); at 3.9°C, the contraction threshold was –44 mV for long depolarizing pulses (100-ms) and increased to +64 mV for 2-ms depolarizations. Hyperpolarizing postpulses shifted the threshold for 2-ms pulses to more positive values, and a similar, but smaller, effect was produced by hyperpolarizing prepulses. The decay of excitability following subthreshold pulses showed two apparently distinct components; at 3.9°C, excitability fell to 50% of its initial value within 4 ms, while the subsequent decline of excitability proceeded with a half-time of about 20 ms.
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1 June 1974
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June 01 1974
Contractile Activation in Frog Skeletal Muscle
L. L. Costantin
L. L. Costantin
From the Department of Physiology and Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
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L. L. Costantin
From the Department of Physiology and Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110
Received:
January 25 1974
Online ISSN: 1540-7748
Print ISSN: 0022-1295
1974
J Gen Physiol (1974) 63 (6): 657–675.
Article history
Received:
January 25 1974
Citation
L. L. Costantin; Contractile Activation in Frog Skeletal Muscle . J Gen Physiol 1 June 1974; 63 (6): 657–675. doi: https://doi.org/10.1085/jgp.63.6.657
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