MOUSE ALVEOLAR SURFACTANT - CHARACTERIZATION OF SUBTYPES PREPARED BY DIFFERENTIAL CENTRIFUGATION

To characterize the properties of alveolar surfactant subfractions obt ained from mouse lung by differential centrifugation, lavage fluid, fo llowing a preliminary centrifugation at 140 X g for 5 min to yield a c ellular pellet (Pc), was sequentially centrifuged at 10,000 X g for 30 min, 60,000 X g for 60 min and 100,000 X g for 15 h; and the resultan t pellets, respectively referred to as P10, P60 and P100, were harvest ed for electron microscopy, phospholipid analysis and surface tension measurements. Ultrastructural differences were observed, in that P10 c ontained large multilamellated structures which were typical of newly secreted surfactant, P100 contained small unilamellar vesicular struct ures, typical of catabolic end products of alveolar surfactant and P60 appeared to contain a mixture of structures present in P10 and P100 i n addition to numerous, large unilamellar vesicles which were not pres ent in either P10 or P100. Slight but significant differences were fou nd in the phospholipid compositions of the three subfractions but not in the fatty acid composition of their phosphatidylcholine (PC) compon ent. There were no significant differences in their disaturated PC/tot al PC ratios, but significant differences in their phospholipid/protei n ratios. P60 had the highest proportion of phospholipid to protein. P 10 and P60 demonstrated surface activity but P100 did not. Total alveo lar surfactant phospholipid was evenly distributed among the three fra ctions. This pattern of distribution was significantly different from that observed in rabbit subfractions prepared by the same procedure. T hese data indicate that mouse alveolar surfactant consists of three di stinct subfractions or subtypes which can be separately and quantitati vely isolated by differential centrifugation. They also suggest that t here may be species differences in the relative proportions of the ind ividual subtypes present in normal adult lung.