Related Experiment Video
Updated: Jun 6, 2026

High-Resolution Fluoro-Respirometry of Equine Skeletal Muscle
Published on: February 3, 2023
Moderate and high intensity sprint exercise induce differential responses in COX4I2 and PDK4 gene expression in
E W Hill1, S S Eivers, B A McGivney
1Animal Genomics Laboratory, UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Dublin 4, Ireland. Emmeline.Hill@ucd.ie
Reasons For Performing Study:
The role of molecular signalling pathways in the phenotypic adaptation of skeletal muscle to different exercise stimuli in the Thoroughbred horse has not been reported previously.
Objective:
To examine CKM, COX4I1, COX4I2 and PDK4 gene expression following high intensity sprint and moderate intensity treadmill exercise stimuli in skeletal muscle of Thoroughbred horses.
Materials And Methods:
Two groups of trained 3-year-old Thoroughbred horses participated. Group A (n = 6 females, n = 3 males) participated in an incremental step test (moderate intensity) to fatigue or HR(max) on a Sato high speed treadmill (distance = 5418.67 m ± 343.21). Group B (n = 8 females) participated in routine 'work' (sprint) on an all-weather gallop (distance = 812.83 m ± 12.53). Biopsy samples were obtained from the gluteus medius pre-exercise (T(0)), immediately post exercise (T(1)) and 4 h post exercise (T(2)). For physiological relevance venous blood samples were collected to measure plasma lactate and creatine kinase concentrations. Changes in mRNA expression were determined by quantitative real-time RT-PCR for creatine kinase muscle (CKM), cytochrome c oxidase subunit IV isoform 1 (COX4I1), cytochrome c oxidase subunit IV isoform 2 (COX4I2) and pyruvate dehydrogenase kinase, isozyme 4 (PDK4) genes. Statistical significance (α < 0.05) was determined using Student's t tests.
Results:
COX4I2 mRNA expression decreased significantly in Group A and remained unchanged in Group B between T(0) vs. T(2) (-1.7-fold, P = 0.017; -1.0-fold, P = 0.859). PDK4 mRNA expression increased significantly in Group B but not in Group A between T(0) vs. T(1) (3.8-fold, P = 0.039; 1.4-fold, P = 0.591). There were no significant changes in the expression in CKM or COX4I1 mRNA abundance in either group.
Conclusions:
Different exercise protocols elicit variable transcriptional responses in key exercise relevant genes in equine skeletal muscle due to variation in metabolic demand.
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