Fatty acid translocase/CD36 mediates the uptake of palmitate by type II pneumocytes

Type II pneumocytes, which synthesize, store, and secrete pulmonary surfact ant, require exogenous fatty acids, in particular palmitic acid, for maximu m surfactant synthesis. The uptake of palmitate by type II pneumocytes is t hought to be protein mediated, but the protein involved has not been charac terized. Here we show by RT-PCR and Northern blot analysis that rat type II pneumocytes express the mRNA for fatty acid translocase (FAT/CD36), a memb rane-associated protein that is known to facilitate the uptake of fatty aci ds into adipocytes. The deduced amino acid sequence from rat type II pneumo cytes reveals 98% identity to the FAT/CD36 sequence obtained from rat adipo cytes. The uptake of palmitate by type II pneumocytes follows Michaelis-Men ten kinetics (Michaelis-Menten constant = 11.9 +/- 1.8 nM; maximum velocity = 62.7 +/- 5.8 pmol.min(-1).5 x 10(5) pneumocytes-l) and decreases reversi bly under conditions of ATP depletion to 35% of control uptake. Incubation of cells at 0 degrees C inhibited the uptake of palmitate almost completely , whereas depletion of potassium was without effect. Preincubation of the c ells with bromobimane or phloretin decreases the uptake of palmitate signif icantly as does preincubation with sulfo-N-succinimidyl oleate, the specifi c inhibitor of FAT/CD36 (C. M. Harmon, P. Luce, A. H. Beth, and N. A. Abumr ad. J. Membr. Biol. 121: 261-268, 1991). From these data, we conclude that FAT/CD36 is expressed in type II pneumocytes and mediates the uptake of pal mitate in a saturable and energy-dependent manner. The data suggest that th e uptake process is independent of the formation of coated pits and endocyt otic vesicles.