Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery

Abstract

AR, Ouyang J. Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery. Am J Physiol Regul Integr Comp Physiol 295: R1238 -R1250, 2008. First published July 23, 2008 doi:10.1152/ajpregu.00171.2008This study investigated the responses in substrate-and energy-based properties to repetitive days of prolonged submaximal exercise and recovery. Twelve untrained volunteers (V O 2peak ϭ 44.8 Ϯ 2.0 ml ⅐ kg Ϫ1 ⅐ min Ϫ1 , mean Ϯ SE) cycled (ϳ60 V O2peak) on three consecutive days followed by 3 days of recovery. Tissue samples were extracted from the vastus lateralis both pre-and postexercise on day 1 (E1), day 3 (E3), and during recovery (R1, R2, R3) and were analyzed for changes in metabolism, substrate, and enzymatic and transporter responses. For the metabolic properties (mmol/kg Ϫ1 dry wt), exercise on E1 resulted in reductions (P Ͻ 0.05) in phosphocreatine (PCr; 80 Ϯ 1.9 vs. 41.2 Ϯ 3.0) and increases (P Ͻ 0.05) in inosine monophosphate (IMP; 0.13 Ϯ 0.01 vs. 0.61 Ϯ 0.2) and lactate (3.1 Ϯ 0.4 vs. 19.2 Ϯ 4.3). At E3, both IMP and lactate were lower (P Ͻ 0.05) during exercise. For the transporters, the experimental protocol resulted in a decrease (P Ͻ 0.05) in glucose transporter-1 (GLUT1; 29% by R1), an increase in GLUT4 (29% by E3), and increases (P Ͻ 0.05) for both monocarboxylate transporters (MCT) (for MCT1, 23% by R2 and for MCT4, 18% by R1). Of the mitochondrial and cytosolic enzyme activities examined, cytochrome c oxidase (COX), and hexokinase were both reduced (P Ͻ 0.05) by exercise at E1 and in the case of hexokinase and phosphorylase by exercise on E3. With the exception at COX, which was lower (P Ͻ 0.05) at R1, no differences in enzyme activities existed at rest between E, E3, and recovery days. Results suggest that the glucose and lactate transporters are among the earliest adaptive responses of substrate and metabolic properties studied to the sudden onset of regular lowintensity exercise. contractile activity; glucose; lactate; transporters; vastus lateralis; glycogen; energy metabolism; enzyme activity IN WORKING SKELETAL MUSCLE, regular submaximal contractile activity promotes a better matching between ATP supply and ATP utilization, resulting in less of a disturbance in phosphorylation potential, increased delivery of fuels, such as carbohydrate (CHO) to the metabolic pathways so as not to be limiting to pathway flux, and attenuation of the by-products of metabolism, such as lactic acid, thereby minimizing their potentially disruptive effects (38,39,46,56,68).It has also been reported that these altered responses depend on a series of adaptations that increase the abundance of a multitude of proteins and protein isoforms that are involved in oxidative phosphorylation (OXPHOS), substrate availability, and metabolic by-product management. The tighter metabolic coupling, as an example, has been attributed to the increase in the potential for OXPHOS, which is believed to occur as a result of increases in mitochondrial density and the maximal ac...

An Official American Thoracic Society/European Respiratory Society Statement: Update on Limb Muscle Dysfunction in Chronic Obstructive Pulmonary Disease

“…Consistent with altered oxidative profile, the limb muscle metabolic profile exhibits, at rest, low concentrations of high-energy phosphates such as ATP and creatine phosphate as well as lower aerobic enzyme activity compared with agematched healthy control subjects (197,198). In addition, intermediate markers of glycolysis, namely glucose-6-phosphate, glucose-1-phosphate, and fructose-6-phosphate as well as phosphofructokinase, and lactate dehydrogenase activities are elevated in resting COPD muscles (198,199).…”

“…The greater reliance on glycolysis can, in part, be explained by the reduced proportion of type I fibers (444, 445) and the lower oxidative enzyme capacities observed in the quadriceps compared with age-matched healthy subjects (190,199) as well as by the higher phosphofructokinase activity observed in COPD (199). Moreover, an additional component of glycolytic reliance might be related to lactate and glucose transporters, whose activity was found be altered in COPD (198). Because these transporters are crucial for lactate removal and glucose entry in limb muscle, they could influence the relative contribution of the glycolytic pathway to the total energy expenditure during exercise.…”

Muscle metabolic, enzymatic and transporter responses to a session of prolonged cycling

“…Within each leg, the sites used for the sampling were randomized. The biopsy sites were prepared as described (Green et al 2008a) and two separate samples using different needles, were obtained from each site. The first sample was rapidly extracted and immediately plunged into liquid N 2 .…”

“…Accordingly, to minimize the contaminating effects of blood and connective tissue on concentration, we have corrected all values to the average TCr, calculated for each individual. Additional analytic information for these measurements appears earlier (Green et al 2007b(Green et al , 2008a.…”

“…Tissue protein was measured (Schacterle and Pollock 1973) and enzyme concentration expressed per unit protein. For COX, a separate protocol was employed with the activity of the enzyme determined spectrophotometrically (Green et al 2008a). As with the metabolites, individual enzymes were measured in blocks with all samples for a given subject analyzed together.…”