TRANSFECTION OF L6 MYOBLASTS WITH ADIPOCYTE FATTY-ACID-BINDING PROTEIN CDNA DOES NOT AFFECT FATTY-ACID UPTAKE BUT DISTURBS LIPID-METABOLISMAND FUSION

We studied the involvement of fatty acid-binding protein (FABP) in gro wth, differentiation and fatty acid metabolism of muscle cells by lipo fection of rat L6 myoblasts with rat heart (H) FABP cDNA or with rat a dipocyte (A) FABP cDNA in a eukaryotic expression vector which contain ed a puromycin acetyltransferase cassette. Stable transfectants showed integration into the genome for all constructs and type-specific over expression at the mRNA and protein level for the clones with H-FABP an d A-FABP cDNA constructs. The rate of proliferation of myoblasts trans fected with rat A-FABP cDNA was 2-fold higher compared with all other transfected cells. In addition, these myoblasts showed disturbed fusio n and differentiation, as assessed by morphological examination and cr eatine kinase activity. Uptake rates of palmitate were equal for all c lone types, in spite of different FABP content and composition. Palmit ate oxidation over a 3 h period was similar in all clones from growth medium. After being cultured in differentiation medium, mock-and H-FAB P-cDNA-transfected cells showed a lower fatty acid-oxidation rate, in contrast with A-FABP-cDNA-transfected clones. The ratio of [C-14]palmi tic acid incorporation into phosphatidylcholine and phosphatidylethano lamine of A-FABP-cDNA-transfected clones changed in the opposite direc tion in differentiation medium from that of mock-and H-FABP-cDNA-trans fected clones. In conclusion, transfection of L6 myoblasts with A-FABP cDNA does not affect H-FABP content and fatty acid uptake, but change s fatty acid metabolism. The latter changes may be related to the obse rved fusion defect.