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Titolo:
CHANGES IN THE MAXIMUM SPEED OF SHORTENING OF FROG-MUSCLE FIBERS EARLY IN A TETANIC CONTRACTION AND DURING RELAXATION
Autore:
JOSEPHSON RK; EDMAN KAP;
Indirizzi:
LUND UNIV,DEPT PHARMACOL,SOLVEGATAN 10 S-22362 LUND SWEDEN UNIV CALIF IRVINE,DEPT PSYCHOBIOL IRVINE CA 92697
Titolo Testata:
Journal of physiology
fascicolo: 2, volume: 507, anno: 1998,
pagine: 511 - 525
SICI:
0022-3751(1998)507:2<511:CITMSO>2.0.ZU;2-T
Fonte:
ISI
Lingua:
ENG
Soggetto:
FORCE-VELOCITY RELATION; SARCOMERE-LENGTH; SKELETAL-MUSCLE; ISOMETRIC TENSION; FIBERS; FATIGUE; CALCIUM; RABBIT; CELLS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
29
Recensione:
Indirizzi per estratti:
Citazione:
R.K. Josephson e K.A.P. Edman, "CHANGES IN THE MAXIMUM SPEED OF SHORTENING OF FROG-MUSCLE FIBERS EARLY IN A TETANIC CONTRACTION AND DURING RELAXATION", Journal of physiology, 507(2), 1998, pp. 511-525

Abstract

1. Isotonic shortening velocities at very light loads were examined in single fibres of the anterior tibialis muscle of the frog, Rana temporaria, using load-clamp recording and slack tests (temperature, 1-3 degrees C; initial sarcomere length, 2.25 mu m). 2. Shortening velocities at very light loads (for ce-clamp recording) were found to be higher early in the rise of a tetanic contraction than during the plateau of the contraction. The upper limit of the load at which there was elevated shortening velocity early in the contraction was 1.5-5.4% of the maximum tetanic tension (F-0) depending on the particular fibre. 3. The maximum shortening velocity determined using the slack test method (V-0) was as much as 30% greater early in a contraction than at the tetanic plateau. V-0 was elevated above the plateau level up to about 30 ms after the end of the latent period, which is equivalent to the timerequired for the force in an isometric contraction to rise to about 30% of F-0. V-0 is depressed below the plateau value during relaxation at the cessation of stimulation. 4. Simulation studies show that the cross-bridge model of Huxley (1957) predicts the maximum shortening velocity to be greater early in a contraction, when new actin binding sites are becoming activated and new croos-bridge connections are being formed rapidly than during steady-state contraction. The elevated shortening velocity in the model is a consequence of new cross-bridges being formed in the pulling configuration, and there being a delay before the newly added bridges are dragged beyond their equilibrium position so they begin to retard shortening. The model also predicts that maximum shortening velocity should be depressed below the plateau level during early relaxation as cross-bridge binding sites are rapidly removedfrom the active population.

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Documento generato il 06/04/20 alle ore 08:26:50