Reasons for performing study: In exercising horses, up to 50% of blood lactate is taken up into red blood cells (RBCs). Lactate transporter proteins MCT1, MCT2 and CD147 (an ancillary protein for MCT1) are expressed in the equine RBC membrane. In Standardbreds (SB), lactate transport activity is bimodally distributed and correlates with the amount of MCT1 and CD147. About 75% of SB studied have high lactate transport activity in RBCs. In other breeds, the distribution of lactate transport activity is unknown.
Objectives: To study whether similar bimodal distribution of MCT1 and CD147 is present also in the racing Finnhorse (FH) and Thoroughbred (TB) as in the SB and to study the distribution of MCT2 in all 3 breeds and to determine if there is a connection between MCT expression and performance markers in TB racehorses.
Methods: Venous blood samples were taken from 118 FHs, 98 TBs and 44 SBs. Red blood cell membranes were purified and MCT1, MCT2 and CD147 measured by western blot. The amount of transporters was compared with TB performance markers.
Results: In TBs, the distribution of MCT1 was bimodal and in all breeds distribution of MCT2 unimodal. The amount of CD147 was clearly bimodal in FH and SB, with 85 and 82% expressing high amounts of CD147. In TBs, 88% had high expression of CD147 and 11% low expression, but one horse showed intermediate expression not apparent in FH or SB. Performance markers did not correlate with the amount of MCT1, MCT2 or CD147.
Conclusions: High lactate transport activity was present in all 3 racing breeds, with the greatest proportion in the TB, followed by the racing FH, then SB. There was no significant statistical correlation found between lactate transporters in RBC membrane and markers of racing performance in the TB.