LACTATE H+ TRANSPORT IN SKELETAL-MUSCLE FROM SPINAL-CORD-INJURED PATIENTS/

In order to evaluate the effect of prolonged muscle inactivity on sarc olemmal lactate/H+ transport in humans, the lactate/H+ transport capac ity was determined in the thigh muscle of spinal-cord-injured (SCI) in dividuals. The lactate transport rate was measured in sarcolemmal gian t vesicles produced by collagenase treatment of muscle biopsies obtain ed from the vastus lateralis muscle. Six SCI subjects with total loss of motor and sensory functions of their lower limbs participated in th e study. The duration of the injury ranged from 2 to 15 years. The tot al lactate transport rate in the muscle of SCI patients was 46.5+/-2.6 pmol.cm(-2).s(-1) (mean+/-SEM), which corresponds to a 17% lower (P<0 .05) transport rate than that found in healthy, untrained subjects. Th e estimated carrier-mediated lactate/H+ transport capacity was approxi mately 26% lower in the SCI patients than in healthy, untrained subjec ts. The observed muscle lactate/H+ transport capacity of SCI individua ls is in accordance with a positive correlation between the capacity o f the lactate/H+ transporters and the percentage occurrence of slow-tw itch fibres in a muscle, although there seems to be a wide range of tr ansport capacities within each fibre type. The present results show th at the sarcolemmal lactate/ Hf transport capacity is lower in SCI indi viduals than in normally physically active subjects, which indicates t hat prolonged muscle inactivity reduces the lactate/H+ transport capac ity of human muscle.