Fatty Acid Transfer Across the Myocardial Capillary Wall

Interstitial transudate of isolated isometrically working perfused rat hearts was analyzed to investigate fatty acid (FA) release and transfer across the capillary wall. Unsaturated FA were released under certain conditions. Lowering medium FA (16:0) with constant or varying FA/A-ratio (A: albumin) decreased interstitial FA-concentration down to 17% of arterial FA-concentration. This was accompanied by reduced uptake-rate. Transcapillary diffusion-resistance, unless markedly altering, cannot be responsible for this observation. Calculated diffusion-rates of FA and FA* protein-complexes in the endothelial cytoplasm and interstitium indicate that FA-transfer takes place almost exclusively bound to carrier-proteins. The apparent permeability surface-area-values of FA for transendothelial FA-transfer are three orders of magnitude higher than those for sucrose; diffusion-coefficients for FA across the endothelium are close to those in water, excluding substantial diffusion-barrier of the capillary wall. Dissociation-rate-constants calculated from experimental data are in the range of those reported for FA*albumin-complexes in vitro. Thus the observed transcapillary FA-gradients are apparently due to the limited dissociation-rate of the FA*albumin-complex in the intravascular space.