Response to normobaric hypoxia in slow and fast muscles of the rat.

In this study the HIF-1 signaling pathway was comparatively studied in fast (EDL) and slow (soleus) muscles in basal normoxic conditions and under normobaric hypoxia (10% oxygen). In normoxia HIF-1α transcription was determined by Real Time PCR and found similar in EDL and in soleus, whereas HIF-1α dependent transcription, explored by Real Time PCR of VEGF which is known as a HIF-1α regulated gene and by expression of luciferase under control of a HIF1α responsive promoter, was higher in soleus than in EDL muscle. Under normobaric hypoxia conditions, HIF1α mRNA showed a small but significant increase in both EDL and soleus and this change was accompanied by an increase of both VEGF transcription and luciferase expression. Interestingly, the time course of the response VEGF and luciferase to hypoxia was different in EDL compared to soleus and, in addition, some discrepancy was detected between VEGF and luciferase pattern. Taken together the results point to diversity between fast and slow muscles in the HIF-1α signaling pathway both in normoxic and hypoxic conditions.