Objectives: To investigate potential role of HIF-1 in skeletal muscle fiber transition, we used heterogenic knock-out (Het-KO, C57/BL6 x SV129 outbreed) mice. Four wild-type (WT) and 5 Het-KO were treated under intermittent hypoxia. Four WT and 2 Het-KO were untreated control.
Methods: We measured changes in muscle tension and fatigability of the GH in vivo and differences in fiber-types using harvested single fibers.
Results: The geniohyoid muscle harvested from WT mice consists of myosin heavy chain (MHC) 2A and 2B; however, more 2A fibers than 2A/2B or 2B alone. After IH challenge for 5 hrs, a combination of MHC 2A and 2B fibers increased significantly (P < 0.05). However, fatigability of the GH muscle remained unchanged. Muscle tensions measured from the GH muscle of WT were greater than those of Het-KO mice. The geniohyoid muscle harvested from both untreated and treated Het-KO mice consisted of MHC 2A/2B, which indicates IH challenge for 5 hrs did not effect fiber composition of the GH in Het-KO mice. Fatigability and muscle tensions over 120 seconds did not differ, either.
Conclusion: We conclude that IH challenge to Het-KO did not influence composition of fiber-types and fatigability of the GH muscle in C57/BL6 x SV129 outbred mice.