Isolation and characterization of hypertrophic type II cells from the lungs of silica-treated rats

Type II cells isolated from the lungs of rats exposed to silica can be separated into two populations by using centrifugal elutriation. One population, designated type IIA, appears similar to type II cells isolated from control lungs. The second population, designated type IIB, consists of type II cells that are larger than type IIA cells or control type II cells. In addition, the type IIB (or hypertrophic) cells contain lamellar bodies which are larger and more numerous than lamellar bodies in type IIA or control type II cells. After centrifugal elutriation, the type II cell populations were purified by differential adherence on rat IgG-coated culture dishes for biochemical and metabolic studies. Type IIB cells contained elevated amounts of protein and total RNA in comparison to type IIA and control type II cells. Type IIB cells contained approximately 2.5-fold more phospholipid than control type II cells (51.5 +/- 3.0 micrograms/10(6) cells versus 20.5 +/- 4.1 micrograms/10(6) cells). Incorporation of the phospholipid precursors [14C]choline and [3H]palmitate into cellular phosphatidylcholines was also increased in type IIB cells. After 120 minutes of incubation, incorporation of [14C]choline into total phosphatidylcholine by type IIB cells was 250% greater than in controls; at this same time point, incorporation of [3H]palmitate was approximately 150% greater than in controls. Incorporation of [14C]choline into disaturated phosphatidylcholine by type IIB cells was 200% greater than in controls. However, no increased incorporation of [3H]-palmitate into disaturated phosphatidylcholine by type IIB cells was seen. These results suggest that the hypertrophic type II cell is responsible for the increases in surfactant-associated phospholipids in the lungs of rats exposed to silica.