HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 99/1/308    most recent 01361.2004v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Stary, C. M. Articles by Hogan, M. C. Search for Related Content PubMed PubMed Citation Articles by Stary, C. M. Articles by Hogan, M. C.

Intracellular pH during sequential, fatiguing contractile periods in isolated single Xenopus skeletal muscle fibers

Department of Medicine, University of California, San Diego, La Jolla, California

Submitted 8 December 2004 ; accepted in final form 3 March 2005

The purpose of the present study was to test the hypothesis that a preceding contractile period in isolated single skeletal muscle fibers would attenuate the decrease in pH during an identical, subsequent contractile period, thereby reducing the rate of fatigue. Intact single skeletal muscle fibers (n = 9) were isolated from Xenopus lumbrical muscle and incubated with the fluorescent cytosolic H⁺ indicator 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) AM for 30 min. Two identical contractile periods were performed in each fiber, separated by a 1-h recovery period. Force and intracellular pH (pH_i) fluorescence were measured simultaneously while fibers were stimulated (tetanic contractions of 350-ms trains with 70-Hz stimuli at 9 V) at progressively increasing frequencies (0.25, 0.33, 0.5, and 1 contraction/s) until the development of fatigue (to 60% initial force). No significant difference (P < 0.05) was observed between the first and second contractile periods in initial force development, resting pH_i, or time to fatigue (5.3 ± 0.5 vs. 5.1 ± 0.6 min). However, the relative decrease in the BCECF fluorescence ratio (and therefore pH_i) from rest to the fatigue time point was significantly greater (P < 0.05) during the first contractile period (to 65 ± 4% of initial resting values) compared with the second (77 ± 4%). The results of the present study demonstrated that, when preceded by an initial fatiguing contractile period, the rise in cytosolic H⁺ concentration in contracting single skeletal muscle fibers during a second contractile period was significantly reduced but did not attenuate the fatigue process in the second contractile period. These results suggest that intracellular factors other than H⁺ accumulation contribute to the fall in force development under these conditions.

anaerobic metabolism; glycolysis; oxidative phosphorylation; phosphocreatine; fluorescence; onset kinetics; exercise

This article has been cited by other articles:

				S. C. Forbes, A. T. Paganini, J. M. Slade, T. F. Towse, and R. A. Meyer Phosphocreatine recovery kinetics following low- and high-intensity exercise in human triceps surae and rat posterior hindlimb muscles Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2009; 296(1): R161 - R170. [Abstract] [Full Text] [PDF]

				B. Walsh, C. M. Stary, R. A. Howlett, K. M. Kelley, and M. C. Hogan Glycolytic activation at the onset of contractions in isolated Xenopus laevis single myofibres Exp Physiol, September 1, 2008; 93(9): 1076 - 1084. [Abstract] [Full Text] [PDF]

				C. M. Stary, B. J. Walsh, A. E. Knapp, D. Brafman, and M. C. Hogan Elevation in heat shock protein 72 mRNA following contractions in isolated single skeletal muscle fibers Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2008; 295(2): R642 - R648. [Abstract] [Full Text] [PDF]

				D. G. Allen, G. D. Lamb, and H. Westerblad Skeletal Muscle Fatigue: Cellular Mechanisms Physiol Rev, January 1, 2008; 88(1): 287 - 332. [Abstract] [Full Text] [PDF]