Elemental composition of lamellar bodies from fetal and adult human lung

Previous studies in the rat using electron probe microanalysis have suggested that most of the Ca2+ in alveolar space is probably derived from secreted lamellar bodies (LB). However, the LB Ca2+ content in cultured rat type II cells is low and unaltered by dexamethasone supplementation. In this study, we examined LB Ca2+ content in adult human lung and cultured explants of fetal lung treated with hormones to promote type II cell differentiation. Lung tissue of 20 to 24 wk of gestation was cultured for 4 to 6 days without hormone and with dexamethasone (10 nM), triiodothyronine (2 nM), 8-bromo-cyclic adenosine monophosphate (0.1 mM), or their combinations. The cultured tissue samples were processed for light and electron microscopy or rapidly frozen and stored in freon-22 under liquid nitrogen. Thin cryosections from the frozen samples were prepared and examined using the electron probe microanalysis. Human lung tissue up to 24 wk of gestational age had no detectable LB before explant culture. Explants cultured for 4 days without hormone supplementation (control) had no detectable LB, single-hormone treatments resulted in small LB, and combination treatments resulted in the formation of many large LB in explant type II cells. Despite such morphologic changes, LB Ca2+ in both control and hormone-treated explants was low (overall mean, 4.1 +/- 0.6; P < 0.05) compared with LB of in situ rat and adult human lung (30 +/- 2 and 27 +/- 1.5 mmol/kg dry wt, respectively) and was similar to that found in cultured rat type II cells. LB phosphorus and sulfur under all explant culture conditions were comparable. These observations indicate that human and rat LB elemental compositions are similar and that optimal in vitro conditions with respect to LB Ca2+ metabolism have not been established.