TRAINING DOES NOT AFFECT ZERO-TRANS LACTATE TRANSPORT ACROSS MIXED RAT SKELETAL-MUSCLE SARCOLEMMAL VESICLES

Hindlimb muscle sarcolemmal vesicles were purified from three age-matched groups of female Sprague-Dawley rats: sedentary control (CON; n = 10), sprint trained (ST; n = 8), and endurance trained (ET; n = 9). Membrane isolations from the three groups were not significantly different in protein yield or purification index. Blood lactate concentration was determined in resting CON rats and running ET and ST rats during the final week. Both the ST and ET groups were significantly higher in citrate synthase (vs. CON) in the soleus and mid-vastus lateralis. The time course of 1 MM L-(+)-lactate uptake in vesicles from the three groups showed no significant difference at any of the five time points tested under zero-trans conditions. Saturation kinetics were examined at nine lactate concentrations, and Lineweaver-Burk plots revealed no difference between groups in apparent Michaelis-Menten constant or maximal transport velocity. Vesicles from CON and ET rats were used to investigate cis inhibition of 0.1 MM L-(+)-lactate transport by four unlabeled monocarboxylates: L-(+)-lactate, D-(-)-lactate, pyruvate, and alpha-cyanohydroxycinnamate at 0.1, 1.0, and 10 mM. Under pH gradient-stimulated L-(+)-lactate transport conditions, cis inhibition was affected by neither D-(-)-lactate nor endurance training. We conclude that the lactate transporter has distinct cis-inhibitory specificity, is stereospecific, and is stimulated when confronted with parallel lactate and proton gradients but that sprint and endurance training do not alter lactate transport rate or capacity under these conditions.