We studied the involvement of fatty acid-binding protein (FABP) in growth, differentiation and fatty acid metabolism of muscle cells by lipofection of rat L6 myoblasts with rat heart (H) FABP cDNA or with rat adipocyte (A) FABP cDNA in a eukaryotic expression vector which contained a puromycin acetyltransferase cassette. Stable transfectants showed integration into the genome for all constructs and type-specific overexpression at the mRNA and protein level for the clones with H-FABP and A-FABP cDNA constructs. The rate of proliferation of myoblasts transfected with rat A-FABP cDNA was 2-fold higher compared with all other transfected cells. In addition, these myoblasts showed disturbed fusion and differentiation, as assessed by morphological examination and creatine kinase activity. Uptake rates of palmitate were equal for all clone types, in spite of different FABP INTRODUCTIONFatty acid-binding proteins (FABPs) belong to a conserved family of intracellular lipid-binding proteins with low molecular mass (14-15 kDa) [1][2][3]. Eight different FABP types have been described : heart, liver, adipose, myelin, intestinal, epidermal, brain and ileal. Many FABP cDNAs have been isolated, cloned and the proteins expressed in bacterial systems. In this way, large amounts of proteins have become available for three-dimensional analysis by crystallography and\or NMR (reviewed in [1,3]). All FABPs studied thus far contain a folding motif designated an up-and-down β-barrel [3].The main function of FABP is thought to be intracellular binding and targeting of fatty acids. FABPs may also modulate the effect of fatty acids on various metabolic enzymes and receptors and cellular processes such as signal transduction and gene expression [1,4]. The function significance of the different FABP types is not clear and may vary with the tissues and the physiological conditions. Adaptation may be related to metabolic requirements of the cell, ligand trafficking and\or modulatory functions.A relation has been observed between fatty acid-oxidation capacity and FABP content of various rat tissues and various human and rat muscles [5][6][7]. FABP content of muscle showed no change under various physiological conditions, except an increase in fast-twitch muscles on chronic electrostimulation and endurance training [7]. Heart FABP (H-FABP) content and fatty acid-oxidation capacity increase in skeletal and heart muscle during postnatal development [7,8]. Some indications of a role Abbreviations used : A-FABP, adipocyte fatty acid-binding protein ; CHO, Chinese hamster ovary ; CK, creatine kinase ; CS, citrate synthase ; D-PBS, Dulbecco's modified PBS ; H-FABP, heart fatty acid-binding protein ; I-FABP, intestinal fatty acid-binding protein ; L-FABP, liver fatty acid-binding protein ; PC, phosphatidylcholine ; PE, phosphatidylethanolamine ; RT, reverse transcriptase ; DMEM, Dulbecco's modified Eagle's medium ; SV40, simian virus 40 ; GAPDH, glyceraldehyde-3-phosphate dehydrogenase ; pac, puromycin acetyltransferase.1 To whom correspondence shou...