Fracture Faces Of Membrane Research Articles

Fracture faces in frozen outer segments from the guinea pig retina.

Outer segments from the retina of the guinea pig have been examined with the freeze-etch technique. In many ways their appearance corroborates previous descriptions of their fine structure. However, the fracture faces of the disc membrane are distinctive and unlike those of any other membrane examined by freeze-etching. One face has the appearance of shallow, irregularly shaped pits surrounded by steep, interconnecting ridges. The other face has the appearance of worn cobblestone pavement. The “stones” are somewhat irregularly shaped, are tightly packed together, and have dimensions of 200–250 A. In transverse fracture, a single disc membrane is represented by a pair of ridges and has a thickness of about 90 A. Evidence is presented that the disc membranes split during fracture and that the two faces seen in freeze-etched replicas are apposed in the intact membrane. This interpretation, assuming fractures split membranes, is compared with one assuming fractures occur along membrane surfaces. The inadequacies of both interpretations are discussed. Plastic deformation can occur during fracture. Such deformation may explain some interpretational difficulties and may account for the lack of perfect match between the two fracture faces in the disc membrane.