Linear arrays of intramembranous particles in pulmonary tubular myelin.

Freeze-fracture preparations of tubular myelin in edematous rat lungs reveal the presence of linear arrays of intramembranous particles. The lines of particles are approximately 50 nm apart and appear to correspond to the intersections of sheets of bilayer membranes. Particles are not seen in lamellar bodies but become evident first in membranes transitional between lamellar bodies and tubular myelin. It is proposed that the particles represent a hydrophobic protein that plays a significant role in the organization of tubular myelin.