Contractions but not AICAR increase FABPpm content in rat muscle sarcolemma.
In the present study, it was investigated whether acute muscle contractions in rat skeletal muscle increased the protein content of FABPpm in the plasma membrane. Furthermore, the effect of AICAR stimulation on FAT/CD36 and FABPpm protein content in sarcolemma of rat skeletal muscle was evaluated.


METHODS
Male wistar rats (150 g) were anesthetized and either subjected to in situ electrically induced contractions (hindlimb muscles: 20 min, 10-20 V, 200 ms trains, 100 Hz) or stimulated with the pharmacological activator of AMPK, AICAR. To investigate changes in the content of FABPpm and FAT/CD36 in the plasma membrane by these stimuli, the giant sarcolemma vesicle (GSV) technique was applied. The hindlimb muscles were removed and used for the production of GSV and lysates. All samples were analyzed using the western blotting technique.


RESULTS
Electrical stimulation of rat hindlimb muscle resulted in an increase in FABPpm protein content in the GSV of 61% (P < 0.05) and in FAT/CD36 protein content in the GSV of 33% (P < 0.05). AICAR stimulation increased FAT/CD36 protein content in GSV by 22% (P < 0.05), whereas FABPpm protein content in GSV was unaffected by AICAR treatment. There was no change in total FAT/CD36 and FABPpm protein expression, measured in lysates with western blotting, by either stimulus. AMPK thr172 and ERK1/2 thr202/204 phosphorylation were significantly increased with muscle contractions (P < 0.05), whereas only AMPK thr172 phosphorylation was increased with AICAR stimulation (P < 0.05).


CONCLUSIONS
These data show that contractions increase both FAT/CD36 and FABPpm protein content in skeletal muscle plasma membrane, whereas only FAT/CD36 protein content is increased when muscle are stimulated with AICAR. This suggests that AMPK is involved in regulation of FAT/CD36, but not FABPpm in skeletal muscle. However, since both ERK1/2 thr202/204 and AMPK thr172 phosphorylation are increased during muscle contractions, the present study cannot rule out that both could play a significant role in regulation of FAT/CD36 and FABPpm during muscle contractions.
Jeppesen
Jacob
J
Molecular Physiology Group, Section of Human Physiology, Copenhagen Muscle Research Centre, Department of Exercise and Sports Sciences, The August Krogh Building, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen, Denmark.
Albers
Peter
P
Luiken
Joost J
JJ
Glatz
Jan F C
JF
Kiens
Bente
B
D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D018955:CD36 Antigens / Q000378:metabolism; D050556:Fatty Acid-Binding Proteins / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D012265:Ribonucleotides / Q000494:pharmacology*; D012508:Sarcolemma / Q000378:metabolism*
D018955:CD36 Antigens; D050556:Fatty Acid-Binding Proteins; D051275:Glucose Transporter Type 4; C515999:Got2 protein, rat; D012265:Ribonucleotides; C495694:Slc2a4 protein, rat; D000620:Aminoimidazole Carboxamide; D006003:Glycogen; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide