Quantitation of phosphatidylcholine secretion in lung slices and primary cultures of rat lung cells

Abstract

Rat lung slices and isolated rat lung cells were used to study the secretion of phosphatidylcholine by the lung in vitro. The rate of incorporation of [3H1choline by lung slices was 20-fold greater than by liver slices and 4fold greater in lung cells compared to confluent skin fibroblasts. Labeling lung slices or cells with [3H choline for up to 8 hr failed to reveal a significant amount of labeled phosphatidylcholine in the medium of either system compared to the medium from liver slice or fibroblast controls. Labeling of isolated lung cells for up to 24 hr, with or without 10% fetal calf serum, also showed no significant difference in the amount of labeled phosphatidylcholine in the medium compared to control fibroblast cultures. Washing labeled lung slices or cells with a nonlysing concentration of Triton X-100 (0.05%) did not selectively release labeled phosphatidylcholine, indicating that any secreted phosphatidylcholine did not adhere to the surface of the lung slices or cells. Experiments were performed to determine whether the small amount of phosphatidylcholine in the medium and detergentreleased phosphatidylcholine was similar to the tissue and cell phosphatidylcholine. The saturated fatty acid composition of the phosphatidylcholine released by Triton X-100 and in the medium (from lung slices) was identical to that of the tissue phosphatidylcholine. In addition, the relative labeling rates of the phospholipids released by Triton X-100 and in the medium (labeled with [14C]glycerol) were identical to those of the tissue and cell phospholipids. Based on these results, we conclude that phosphatidylcholine is not secreted by lung slices and lung cells in large amounts compared to controls. The implication of these data is that pulmonary surfactant material may actually not be secreted by the lung in vitro, and perhaps in vivo, in the manner that is currently generally accepted.Differentiated lung apparently secretes a mixture of phospholipid and protein known as pulmonary surfactant that prevents alveolar collapse by providing a relatively low surface tension at the air-alveolar interface. Dipalmitoylphosphatidylcholine is the major component of surfactant and seems to be responsible for most of its surface tension-lowering properties. The accumulation of phosphatidylcholine (PC) in phospholipid obtained by lung lavage (surfactant) has been studied thoroughly in vivo primarily by pulse-labeling intact animals with a radioactive phospholipid precursor followed by quantitation of labeled PC in recovered surfactant (1-4). Unfortunately, disaturated PC is ubiquitous in tissues (5) and is synthesized, and even released, by fibroblasts in vitro (6). Thus, disaturated PC may not be a truly specific marker for surfactant production in vitro. Some studies in vitro have only quantitated PC labeling in tissue slices or cells and presented no data on secretion (7-9). In other studies, disaturated PC synthesis and its release to the medium have been assumed to be specific markers for surfactant production (10-13...

Identification of osmo‐dependent and osmo‐independent betaine‐choline‐carnitine transporters in Acinetobacter baumannii: role in osmostress protection and metabolic adaptation

“…The most abundant source of choline in the human host is the choline headgroup moiety of phosphatidylcholine (PC) and sphingomyelin (SM) which form 50% to 90% of the phospholipids in the outer leaflet of eukaryotic plasma membranes (Zachowski, 1993). Especially the membranes of lung epithelial cells are choline rich and consist of up to 70% PC (Keller and Ladda, 1979). Cleavage of PC or SM by phospholipases D (PLD) or phospholipases C (PLC) liberates choline and phosphorylcholine, respectively (Holbrook et al, 1991;Fiester et al, 2016).…”

The carnitine degradation pathway ofAcinetobacter baumanniiand its role in virulence

“…The latter are very abundant in human hosts such as choline is the head group moiety of phosphatidylcholine (PC) and sphingomyelin which form 50%–90% of the phospholipids in the outer leaflet of eukaryotic plasma membranes (Zachowski, 1993). Especially the membranes of lung epithelial cells are choline rich and consist of up to 70% PC (Keller and Ladda, 1979). Carnitine is also very abundant in human host tissues and is found in blood, liver, kidney, brain and heart.…”