Transfer of [l- 14C] palmitate between myocardial cell fractions

Abstract

Mitochondrial, microsomal and cytoplasmic fractions from the heart, labelled with [1- 14C] palmitate, have been added to non-radioactive myocardial homogenate and the distribution of lipid radio-activity between the three cell fractions determined. During the course of rehomogenisation and cell fractionation at 4°C a substantial movement of lipid radioactivity occurred between all three fractions. Expressed as lipid radioactivity/mg protein the activity of the microsomal fraction was greatest. This appears to be due to the rapid incorporation of radioactive fatty acid into phospholipid in the microsomal fraction. After perfusion of isolated rat hearts with [1- 14C] palmitate complexed to albumin for 15 s at 4°C over 90% of the radioactivity of the mitochondrial and cytoplasmic fractions was present in free fatty acids. This figure was significantly lower in the microsomal fraction where some 15% of the radioactivity was already present in phospholipid. Washing mitochondrial and microsomal fractions with albumin solution removed more lipid radioactivity than washing with sucrose solution and removed a greater proportion of radioactivity from free fatty acids than from phospholipid. It is concluded that during perfusion or during cell-fractionation at 4°C free fatty acids transfer rapidly between subcellular components. The rapid incorporation of radioactive fatty acids into phospholipid in the microsomal fraction decreases the mobility of label from this fraction.