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Purpose: This study was designed to probe the effect of downhill running on microtubule acetylation and autophagic flux in rat skeletal muscle. Methods : Sprague-Dawley rats were subjected to an exercise protocol of a 90-min downhill run with a slope of -16[degrees] and a speed of 16 m[middle dot]min-1, and then the soleus was sampled at 0, 12, 24, 48, and 72 h after exercise. Protein expression levels of microtubule-associated protein 1 light chain 3 (LC3), p62/sequestosome 1 (p62), [alpha]-tubulin, and acetylated [alpha]-tubulin (AcK40 [alpha]-tubulin) were detected by Western blotting. Alpha-tubulin was costained with AcK40 [alpha]-tubulin or cytoplasmic dynein intermediate chain in a single muscle fiber, and LC3 was costained with lysosomal-associated membrane protein 1 in cryosections. To assess autophagic flux in vivo , colchicine or vehicle was injected intraperitoneally 3 d before the exercise experiment, and the protein levels of LC3 and p62 were measured by Western blotting. Results : Downhill running induced a significant increase in the protein levels of LC3-II and p62, whereas the level and proportion of AcK40 [alpha]-tubulin were markedly decreased. Furthermore, the amount of dynein on [alpha]-tubulin was decreased after downhill running, and autophagosomes accumulated in the middle of myofibrils. Importantly, LC3-II flux was decreased after downhill running compared with that in the control group. Conclusions: A bout of downhill running decreases microtubule acetylation, which may impair dynein recruitment and autophagosome transportation, causing blocked autophagic flux. [ABSTRACT FROM AUTHOR]