Lamellar bodies of type II alveolar epithelial cells are the intracellular storage sites of lung surfactant, while tubular myelin figures are an extracellular surfactant form found in the alveolar fluid. A refined procedure was used to isolate intact lamellar bodies from rat lung homogenates in a fraction of high purity and yield. The stability of isolated lamellar bodies under various conditions was determined by electron microscopy. Lamellar bodies were completely disrupted after incubation at 37, 24, and 0 degrees C for 0.6, 2, and 12 hr, respectively, in 0.33 M sucrose, 0.01 M HEPES (pH 7.4). In addition, they were completely disrupted after incubation for 1 hr in 0.33 M sucrose, 1 mM EGTA at 0 degrees C or 0.154 M NaCl or 0.10 M sodium phosphate (pH 7.4) at 24 degrees C. Incubation of isolated lamellar body fractions in medium containing 5 mM Ca++ or Mg++ at 37 degrees C for 1 hr resulted in the appearance of tubular myelin figures. A procedure is also presented for the isolation of tubular myelin figures from rat lung lavage fluid.

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A comparison of the occurrence, fatty acid composition, and metabolism of phosphatidyglycerol and phosphatidylcholine in the surfactant and residual fraction of rat lung has been carried out. The surfactant and residual fractions were separated by discontinuous sucrose density gradient centrifugation. The surfactant fraction was found to contain 69 percent phosphatidylcholine and 7 percent phosphatidylglycerol. The residual fraction contained 46 percent phosphatidylcholine and 3 percent phosphatidylglycerol. Phosphatidylcholine and phosphatidylglycerol were found to contain 85 and 79 percent palmitate in the surfactant fraction and 67 and 68 percent in the residual fraction, respectively. Isolated rat lungs were perfused with medium containing [U-14C]glucose, [9,10-3H]palmitate, and [1-14C]acetate and the incorporation into palmitate isolated from the alpha and beta position of phosphatidylcholine and phosphatidylglycerol was determined. Each radioactive substrate was found to be incorporated into palmitate of phosphatidylcholine equally at the alpha and beta position of the surfactant fraction. In the residual fraction the specific activity of the beta position palmitate was found to be twice that of the alpha position. The incorporation of [9,10-3H]palmitate and [1-14C]acetate into palmitate at the alpha and beta positions of phosphatidylglycerol was similar in both the surfactant and residual fractions. In each case palmitate at the alpha position had approximately twice the specific activity of that at the beta position. The incorporation of [U-14C]glucose into phosphatidylglycerol of the surfactant fraction was, however, greater in palmitate at the beta position than at the alpha. The results show that phosphatidylglycerol is associated with the lung surfactant fraction and suggest that palmitate esterified to the alpha and beta positions of phosphatidylglycerol and phosphatidylcholine occurs at different rates and is dependent upon the precursor source of palmitate.