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: 98/5/1639    most recent 00874.2004v1 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 ISI Web of Science 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 ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Kindig, C. A. Articles by Hogan, M. C. Search for Related Content PubMed PubMed Citation Articles by Kindig, C. A. Articles by Hogan, M. C.

Effect of contractile duration on intracellular PO₂ kinetics in Xenopus single skeletal myocytes

Department of Medicine, Physiology Division, University of California-San Diego, La Jolla, California

Submitted 12 August 2004 ; accepted in final form 8 January 2005

It has been suggested that skeletal muscle O₂ uptake (O₂) kinetics follow a first-order control model. Consistent with that, O₂ should show both 1) similar onset kinetics and 2) an on-off symmetry across submaximal work intensities regardless of the metabolic perturbation. To date, consensus on this issue has not been reached in whole body studies due to numerous confounding factors associated with O₂ availability and fiber-type recruitment. To test whether single myocytes demonstrate similar intracellular PO₂ (PI_O2) on- and off-transient kinetics at varying work intensities, we studied Xenopus laevis single myocyte (n = 8) PI_O2 via phosphorescence quenching during two bouts of electrically induced isometric muscle contractions of 200 (low)- and 400 (high)-ms contraction duration (1 contraction every 4 s, 15 min between trials, order randomized). The fall in PI_O2, which is inversely proportional to the net increase in O₂, was significantly greater (P < 0.05) during the high (24.1 ± 3.2 Torr) vs. low (17.4 ± 1.6 Torr) contraction bout. However, the mean response time (MRT; time to 63% of the overall change) for the fall in PI_O2 from resting baseline to end contractions was not different (high, 77.8 ± 11.5 vs. low, 76.1 ± 13.6 s; P > 0.05) between trials. The initial rate of change at contraction onset, defined as PI_O2/MRT, was significantly greater (P < 0.05) in high compared with low. PI_O2 off-transient MRT from the end of the contraction bout to initial baseline was unchanged (high, 83.3 ± 18.3 vs. low, 80.4 ± 21.6 s; P > 0.05) between high and low trials. These data revealed that PI_O2 dynamics in frog isolated skeletal myocytes were invariant despite differing contraction durations and, by inference, metabolic demands. Thus these findings demonstrate that mitochondria can respond more rapidly at the initial onset of contractions when challenged with an augmented metabolic stimulus in accordance with an apparent first-order rate law.

oxygen consumption; muscle energetics; skeletal muscle fiber

This article has been cited by other articles:

				B. Glancy, T. Barstow, and W. T. Willis Linear relation between time constant of oxygen uptake kinetics, total creatine, and mitochondrial content in vitro Am J Physiol Cell Physiol, January 1, 2008; 294(1): C79 - C87. [Abstract] [Full Text] [PDF]

				P. McDonough, B. J. Behnke, D. J. Padilla, T. I. Musch, and D. C. Poole Respiratory: Control of microvascular oxygen pressures during recovery in rat fast-twitch muscle of differing oxidative capacity Exp Physiol, July 1, 2007; 92(4): 731 - 738. [Abstract] [Full Text] [PDF]

				R. A. Howlett, C. A. Kindig, and M. C. Hogan Intracellular PO2 kinetics at different contraction frequencies in Xenopus single skeletal muscle fibers J Appl Physiol, April 1, 2007; 102(4): 1456 - 1461. [Abstract] [Full Text] [PDF]