ISOLATION AND CHARACTERIZATION OF THE LIPID-CONTAINING INTERSTITIAL CELL FROM THE DEVELOPING RAT LUNG

Abstract

A lipid-containing interstitial cell (LIC) appears in the walls of alveoli during the period of postnatal lung growth associated with the formation of gas exchange surfaces. This cell was isolated from the 10 day neonatal rat lung by digesting the lung with trypsin and collagenase and using a 6% metrizamide discontinuous density gradient. 5.0 .+-. 0.4 .times. 106 LIC per grams of lung wet weight were isolated at 10 days. At this age triglycerides accounted for 65% of the LIC lipid with 62% of the triglyceride fatty acids being unsaturated. Linoleic acid was a prominent triglyceride moiety. Density profiles of LIC isolated from 4, 7, 12, 16 and 21 day neonatal rats, using 0-10% metrizamide continuous density gradients, revealed a 2x increase in LIC numbers between 4 and 7 days, after which LIC numbers decreased linearly until few LIC were observed at the age of weaning. Mean LIC density decreased from 1.045/cm3 at 4 days to 1.036/cm3 at 12 days, but thereafter increased to 1.050/cm3 at 21 days suggesting accumulation and dissipation of cytoplasmic lipid by LIC during the period of lung growth in which alveoli form. Although the origin, role and fate of the LIC and its lipid are uncertain, the unique time of appearance of this distinct interstitial cell suggests that it is involved in alveolar formation and lung restructuring during early postnatal lung development.