Age-Related Changes in Myosin Light and Heavy Chain Isoforms' Composition in Gluteus Medius Muscle of Sedentary Akhal-Teke Horses

The primary purpose of the present study was to examine age dependence of gluteus medius muscle phenotypic plasticity with regard to myosin light chain (MyLC) and myosin heavy chain (MyHC) isoform expression of sedentary Akhal-Teke horses. A total of 23 Akhal-Teke horses (11 horses, 1.5 to 2.5-year-old; nine horses, 9 to 20-year-old; and three horses, 21 to 23.5-year-old) were studied. A muscle biopsy of depth 60 mm from the left gluteus medius muscle was obtained. MyHC and MyLC isoform pattern was determined in three age groups. The current study demonstrated that in the 21 to 23.5-year-old age group, the relative content of MyHC I isoform and MyLC 1slow isoform decreased significantly. The results of the current study indicate that gluteus medius muscle of Akhal-Teke horses consists of a relatively high percentage of MyHC I and IIa isoforms, which together compose about 50% of MyHC. MyHC IIa and IIx isoforms together compose 88% to 94% of MyHC isoforms. Age-related decrease of the relative content of MyHC I and MyLC 1slow isoforms in gluteus medius muscle starts in Akhal-Teke horses older than 20 years.