AJP - Lung Cellular and Molecular Physiology, Vol 261, Issue 4 334-L340, Copyright © 1991 by American Physiological Society

ARTICLES

Alveolar uptake of lipid and protein components of surfactant

A. B. Fisher, C. Dodia and A. Chander
Institut for Environmental Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104-6068.

We investigated the clearance of radiolabeled natural surfactant from the alveolar space of the isolated perfused rat lung. 3H, 35S-natural surfactant was prepared from rat lungs that had been perfused with [methyl-3H]choline and [35S]methionine. The biosynthesized material contained greater than 95% of 3H in phosphatidylcholine (PC) and approximately 80% of 35S in surfactant protein A. Natural surfactant (1 mumol PC) was instilled into the trachea; lungs were analyzed 5 min later or after 2 h perfusion to determine surfactant uptake, defined as lung lavage-resistant 3H or 35S [% of instilled disintegrations per minute(dpm)]. Uptake at 5 min was 31.4 +/- 0.37% for 3H and 31.9 +/- 0.85% for 35S (mean +/- SE, n = 4). At 2 h, uptake was 46.6 +/- 0.96% for 3H and 45.8 +/- 1.1% for 35S (n = 7). In the presence of 0.1 mM 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), uptake at 2 h for both 3H and 35S was stimulated to approximately 57% of instilled dpm (n = 4). Microsomes and plasma membranes isolated from lung homogenates had a ratio of 3H to 35S that was similar to the original surfactant, whereas 3H/35S in isolated lamellar bodies was increased 2.1-fold. Degradation of lipid was indicated by finding 13.4 +/- 0.65% of homogenate 3H in the aqueous fraction of lung extract after 2 h perfusion; only 2.3 +/- 0.47% of 35S dpm were soluble in trichloroacetic acid, suggesting significantly less protein breakdown. Lipid degradation was increased more than twofold by 8-BrcAMP, whereas protein degradation was not changed significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

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