Role of apoprotein and calcium ions in surfactant function.

Pulmonary surfactant isolated in the presence of calcium ions contains substantial amounts of the morphologic structure, tubular myelin. Chelation of these calcium ions results in disruption of this structure and attendant loss of surface adsorption. Reassembly studies indicate that ability of the lipids to rapidly form surface films is dependent on the presence of a specific surfactant protein in addition to the calcium ions. The formation of this surface-active complex (apoprotein-lipid-calcium ions) is accompanied by aggregation of the lipid. This increase in aggregation may have important implications in the mechanism of surfactant function.