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This Article Full Text Full Text (PDF) All Versions of this Article: 90/6/873    most recent expphysiol.2005.031559v1 Alert me when this article is cited Alert me if a correction is posted 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 Howlett, R. A Articles by Hogan, M. C Search for Related Content PubMed PubMed Citation Articles by Howlett, R. A Articles by Hogan, M. C Related Collections Muscle

¹ Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0623, USA ² Department of Health and Human Performance, Auburn University, Auburn, AL 36849, USA ³ Department of Biomedical Sciences and Technology, University of Milan, Italy

In isolated single skeletal myocytes undergoing long-term fatiguing contractions, caffeine (CAF) can result in nearly immediate restoration of generated tension to near-prefatigue levels by increasing Ca²⁺ release via activation of sarcoplasmic reticulum release channels. This study tested whether arterial CAF infusion (>5 mM) would cause a similar rapid restoration of tetanic isometric tension during contractions to fatigue in perfused canine hindlimb muscle in situ. Tetanic contractions were elicited by electrical stimulation (200 ms trains, 50 Hz, 1 contraction s^–1), and biopsies were taken from the muscle at rest and during contractions: (1) following the onset of fatigue (tension 60% of initial value); and (2) following CAF administration. Resting muscle ATP, PCr and lactate contents were 25.2 ± 0.4, 76.9 ± 3.3 and 14.4 ± 3.3 mmol (kg dry weight)^–1, respectively. At fatigue, generated tetanic tension was 61.1 ± 6.9% of initial contractions. There was a small but statistically significant recovery of tetanic tension (64.9 ± 6.6% of initial value) with CAF infusion, after which the muscle showed incomplete relaxation. At fatigue, muscle ATP and PCr contents had fallen significantly (P < 0.05) to 18.1 ± 1.1 and 18.9 ± 2.1 mmol (kg dry weight)^–1, respectively, and lactate content had increased significantly to 27.7 ± 5.4 mmol (kg dry weight)^–1. Following CAF, skeletal muscle ATP and PCr contents were significantly lower than corresponding fatigue values (15.0 ± 1.3 and 10.9 ± 2.2 mmol (kg dry weight)^–1, respectively), while lactate was unchanged (22.2 ± 3.9 mmol (kg dry weight)^–1). These results demonstrate that caffeine can result in a small, but statistically significant, recovery of isometric tension in fatigued canine hindlimb muscle in situ, although not nearly to the same degree as seen in isolated single muscle fibres. This suggests that, in this in situ isolated whole muscle model, alteration of Ca²⁺ metabolism is probably only one cause of fatigue.

(Received 13 July 2005; accepted after revision 17 August 2005; first published online 23 August 2005)
Corresponding author R. A. Howlett: Department of Medicine, MC0623A, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA. Email: rhowlett{at}ucsd.edu

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