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This Article Full Text Full Text (PDF) All Versions of this Article: 92/5/887    most recent expphysiol.2007.037291v1 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.

¹ Department of Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA

This study investigated the relationship between hypoxia and the rate of fatigue development in contracting rat hindlimb muscles composed primarily of different fibre types. Hindlimb muscles of 11 rats were exposed, and the soleus (SOL) and gastrocnemius/plantaris (GP) were each isolated with circulation intact and attached to individual force transducers. Rats were then equilibrated with either normoxic (N; arterial partial pressure of O₂ 87.7 ± 1.5 mmHg) or hypoxic conditions (H; arterial partial pressure of O₂ 30.0 ± 2.4 mmHg) using an inspired O₂ fraction of 0.21 and 0.10, respectively. The stimulation protocol consisted of 2 min each at 0.125, 0.25, 0.33 and 0.5 tetanic contractions s^–1 sequentially for both conditions. Following the 8 min stimulation period, relative developed muscle tension (% of maximal) was nearly identical for both H and N in SOL (54.2 ± 3.5 versus 54.3 ± 4.2%), but was significantly (P < 0.05) lower in H than N (10.8 ± 0.9 versus 43.0 ± 8.9%) in GP, indicating a greater amount of fatigue during hypoxia only in the GP. Soleus phosphocreatine (PCr) content fell to similar levels (24.1 ± 1.6 versus 21.1 ± 4.9 mmol (kg dry weight (dw))^–1) during both H and N, but in the white portion of the gastrocnemius (WG), PCr was significantly lower following H than N (14.3 ± 1.5 versus 34.0 ± 6.0 mmol (kg dw)^–1). Similarly, muscle lactate increased in both fibre types at fatigue, but only in WG was the increase significantly greater with H (SOL 7.1 ± 2.0 versus 5.3 ± 1.1 mmol (kg dw)^–1; WG 13.7 ± 4.5 versus 5.3 ± 2.2 mmol (kg dw)^–1). Increases in calculated muscle [H⁺], free ADP and free AMP were similar between N and H in SOL but were significantly greater during H compared with N in WG. These data demonstrate that hypoxia induces greater fatigue and disruption of cellular homeostasis in rat hindlimb muscle composed primarily of fibres with low oxidative capacity compared with those of a more oxidative type.

(Received 11 February 2007; accepted after revision 23 May 2007; first published online 1 June 2007)
Corresponding author M. C. Hogan: Department of Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA. Email: mchogan{at}ucsd.edu

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