PHOSPHATIDYLCHOLINE (PC) SECRETION BY CULTURED FETAL RAT TYPE II PNEUMOCYTES

Abstract

Purinooeptor and B-adrenergio agonists have been shown to stimulate PC secretion by adult rat type II cells. We have studied the influence of these agents on secretion by fetal type II cells. The cells were isolated by explant culture, cell dissociation, differential adhesion, type II cell aggregation, and monolayer culture. To study secretion the cells were incubated with [3H]-choline for 20h, followed by 90 minutes of exposure to varying concentrations of ATP or terbutaline. Purity of type II cell cultures ranged from 85 to 90%. Post culture viability was 97.3±0.2%. LDH release averaged 1.5%; no difference was observed between control and treated cultures.Baseline secretion of PC from the fetal cells was 0.63±0.11%. We observed dose dependent enhancement of secretion by both ATP and terbutaline. Maximal stimulation by ATP occurred at 10−4 M. At this dose secretion was 1.24±0.28% (97% increase). Maximal stimulation by terbutaline was observed at 10−5 M (75% increase). These data differ from those in adult rat type II cells in which baseline PC secretion ranged from 1% to 3%. ATP and terbutaline produced greater stimulation in adult cells (approximately 400% and 100% respectively) than in fetal cells.We conclude that fetal type II cells secrete PC. Baseline and stimulated secretion is lower in these cells than in adult cells. This suggests that although fetal and adult cells are morphologically similar, they are functionally different. (Supported by HD 07091, HL 19752, HL 31175.)