Journal of Applied Physiology, Vol 75, Issue 5 2265-2272, Copyright © 1993 by American Physiological Society

ARTICLES

Mechanical determinants of isotonic relaxation in isolated diaphragm muscle

C. Coirault, D. Chemla, N. Pery, I. Suard and Y. Lecarpentier
Institut National de la Sante et de la Recherche Medicale Unite 275-Loa-Ensta-Ecole Polytechnique, Palaiseau, France.

Determinants of lengthening velocity have not been investigated in the diaphragm muscle. This study was undertaken to define the mechanical determinants of isotonic relaxation rate over the entire load continuum in isolated rat diaphragm (n = 30). We tested the hypothesis that the determinants of lengthening could include loading conditions, namely, preload and afterload; abrupt changes of load during the contraction phase; end-shortening muscle length (ESL); extent of shortening (delta L); time; stimulation mode; and stimulation frequency. In afterloaded contractions preloaded at optimal initial length and stimulated in tetanus at 30 Hz, peak lengthening velocity (+dL/dtmax) was linearly related to delta L, ESL, and/or total load. Varying initial muscle length, ESL, afterload, or the load imposed on the muscle during the isotonic lengthening process did not modify +dL/dtmax vs. delta L relationship, whereas +dL/dtmax vs. load and +dL/dtmax vs. ESL relationships were modified by these procedures. For a given delta L, +dL/dtmax could be modified when lengthening was delayed by reversing the relaxation sequence and when twitch and tetanus modes were compared. In conclusion, our results demonstrate that in isolated diaphragm muscle, delta L is the main determinant of +dL/dtmax over a wide range of loads and under various experimental conditions, independent of ESL and initial muscle length and independent of the load imposed on the muscle during the lengthening process. Time and stimulation mode were also shown to modulate the lengthening rate in diaphragm muscle.

This article has been cited by other articles:

				B. Bouhemad, O. Langeron, G. Orliaguet, P. Coriat, and B. Riou Effects of halothane and isoflurane on the contraction, relaxation and energetics of rat diaphragmatic muscle Br. J. Anaesth., September 1, 2002; 89(3): 479 - 485. [Abstract] [Full Text] [PDF]

				G. Orliaguet, O. Langeron, B. Bouhemad, P. Coriat, Y. LeCarpentier, and B. Riou Effects of postnatal maturation on energetics and cross-bridge properties in rat diaphragm J Appl Physiol, March 1, 2002; 92(3): 1074 - 1082. [Abstract] [Full Text] [PDF]

				C. Coirault, D. Chemla, and Y. Lecarpentier Relaxation of diaphragm muscle J Appl Physiol, October 1, 1999; 87(4): 1243 - 1252. [Abstract] [Full Text] [PDF]

				Y. Lecarpentier, C. Coirault, O. Langeron, F. X. Blanc, S. Salmeron, P. Attal, B. Riou, and D. Chemla Impaired load dependence of diaphragm relaxation during congestive heart failure in the rabbit J Appl Physiol, October 1, 1999; 87(4): 1339 - 1345. [Abstract] [Full Text] [PDF]

				F.-X. Blanc, S. Salmeron, C. Coirault, M. Bard, E. Fadel, E. Dulmet, P. Dartevelle, and Y. Lecarpentier Effects of load and tone on the mechanics of isolated human bronchial smooth muscle J Appl Physiol, February 1, 1999; 86(2): 488 - 495. [Abstract] [Full Text] [PDF]

				C. Coirault, D. Chemla, J.-C. Pourny, F. Lambert, and Y. Lecarpentier Instantaneous force-velocity-length relationship in diaphragmatic sarcomere J Appl Physiol, February 1, 1997; 82(2): 404 - 412. [Abstract] [Full Text] [PDF]