Training-induced elevation in FABP_PMis associated with increased palmitate use in contracting muscle

Abstract

To evaluate the effects of endurance training in rats on fatty acid metabolism, we measured the uptake and oxidation of palmitate in isolated rat hindquarters as well as the content of fatty acid-binding proteins in the plasma membranes (FABP(PM)) of red and white muscles from 16 trained (T) and 18 untrained (UT) rats. Hindquarters were perfused with 6 mM glucose, 1,800 microM palmitate, and [1-(14)C]palmitate at rest and during electrical stimulation (ES) for 25 min. FABP(PM) content was 43-226% higher in red than in white muscles and was increased by 55% in red muscles after training. A positive correlation was found to exist between succinate dehydrogenase activity and FABP(PM) content in muscle. Palmitate uptake increased by 64-73% from rest to ES in both T and UT and was 48-57% higher in T than UT both at rest (39.8 +/- 3.5 vs. 26.9 +/- 4. 4 nmol. min(-1). g(-1), T and UT, respectively) and during ES (69.0 +/- 6.1 vs. 43.9 +/- 4.4 nmol. min(-1). g(-1), T and UT, respectively). While the rats were resting, palmitate oxidation was not affected by training; palmitate oxidation during ES was higher in T than UT rats (14.8 +/- 1.3 vs. 9.3 +/- 1.9 nmol. min(-1). g(-1), T and UT, respectively). In conclusion, endurance training increases 1) plasma free fatty acid (FFA) uptake in resting and contracting perfused muscle, 2) plasma FFA oxidation in contracting perfused muscle, and 3) FABP(PM) content in red muscles. These results suggest that an increased number of these putative plasma membrane fatty acid transporters may be available in the trained muscle and may be implicated in the regulation of plasma FFA metabolism in skeletal muscle.

Oxidation of intracellular and extracellular fatty acids in skeletal muscle

“…The lower end of the results [19] [20] [45] are similar to that observed in the present study with muscle incubation. The higher values (but not the highest) [46] [47] are comparable to the results of the present study obtained using the model with 13 C-palmitate tracers. Using muscle homogenate, the results were even lower [48].…”

AMPKα2deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle

“…On the day of the experiment, mice were anesthetized by an intraperitoneal injection of ketamine-xylazine cocktail (20 mg/kg body wt). Surgical preparation for the hindlimb perfusion was performed as previously described (38,49,50). Before placement of the perfusion catheters, heparin (15 IU) was injected into the inferior vena cava.…”

“…Perfusate samples collected during the perfusion were analyzed to determine FA, glucose, and lactate con- (46,48,49). An ABL-5 analyzer (Radiometer America, Westlake, OH) was used to determine PCO2, PO2, and pH.…”

“…Palmitate delivery, fractional and total palmitate uptake, and percent and total palmitate oxidation were calculated as described previously in detail (46,49). Acetate correction factors (49) were used to correct percent and total FA oxidation for label fixation.…”

“…The specific activity for palmitate in the arterial samples was not different between groups and did not vary over time, averaging 153.7 Ϯ 9.8, 160.2 Ϯ 12.6, and 141.9 Ϯ 16.8 Ci/mmol for the resting, caffeine-treated, and muscle contraction groups, respectively (P Ͼ 0.05). O 2 uptake, glucose uptake, and lactate release were calculated as described elsewhere (49). All uptake and release rates are expressed per gram of perfused hindlimb muscles of both legs, which we determined to be ϳ7% of total body weight for WT and DN mice.…”