SKELETAL-MUSCLE GLYCOLYTIC CAPACITY AND PHOSPHOFRUCTOKINASE REGULATION IN HORSES WITH POLYSACCHARIDE STORAGE MYOPATHY

Objective-To determine whether polysaccharide storage myopathy (PSSM) in Quarter Horses is attributable to a defect in glycolysis or in the allosteric regulation of phosphofructokinase (PFK) enzyme. Animals-Mus cle biopsy specimens were obtained from 6 Quarter Horses with PSSM and 8 Quarter Horse or Thoroughbred control horses. Procedures-Maximal ac tivity of glycogenolytic and glycolytic enzymes was determined spectro photometrically. Maximal activity of PFK was determined for each horse at pH 8.0, and at pH 7.0 when variable concentrations of the activato rs, fructose 6 phosphate, fructose 2.6 bisphosphate, and adenosine mon ophosphate or inhibitors adenosine triphosphate and citrate were added to the reaction mixture. Relative activity was calculated as activity at pH 7/maximal PFK activity. Results-Deficiencies in glycogenolytic or glycolytic enzyme activities were not evident in horses with PSSM. Differences between horses with PSSM and control horses in relative ac tivity of PFK were not apparent for any of the activators or inhibitor s used in the study. Conclusions-In a group of horses with PSSM, we we re unable to detect a glycogenolytic or glycolytic enzyme deficiency o r abnormality in the allosteric regulation of PFK. Clinical Relevance- Although PSSM is clinically and histologically similar to glycogenolyt ic/glycolytic enzyme deficiencies in human beings and other animal spe cies, abnormalities in this metabolic pathway are not present in horse s with PSSM.