METABOLIC PROFILES OF CAT AND RAT PHARYNGEAL AND DIAPHRAGM MUSCLES

Pharyngeal muscles play important roles in the maintenance of upper ai rway patency during sleep. The present study determined the extent of heterogeneity among pharyngeal muscles and the diaphragm in their meta bolic profiles, and examined whether differences among muscles may acc ount for previously described differences in their fatigue resistance. Cat and rat sternohyoid, geniohyoid, genioglossus (cat only) and diap hragm muscle were assayed for activities of the mitochondrial enzyme c itrate synthase (CS), the glycolytic enzyme phosphofructokinase (PFK) and the cytosolic enzyme lactate dehydrogenase (LDH). CS activity vari ed among muscles in both species, being highest for genioglossus in ca t and highest for diaphragm in rat. PFK activity was highest for genio glossus in cat, but did not differ among muscles in rat. LDH activity was lower for the genioglossus than the sternohyoid and diaphragm in c at. CS and PFK activities correlated positively, and LDH activity corr elated negatively, with in vitro fatigue resistance assessed after 5 m in of repetitive stimulation in cat. These data indicate close relatio nships between metabolic profiles, particularly oxidative capacity, an d fatigue resistance of pharyngeal muscles in relationship to each oth er and to the diaphragm.