Double-replica topography of disk membrane structures in the carp (Cyprinus carpio).

By an improved freeze-fracture device, a number of double replicas were obtained from the rod disk membranes of the carp retina for investigation of complementary, continuing, and transitional relationships between fracture faces. Some separate particles found along the smooth edge bordering on the adjacent interdisk cytoplasm can be occasionally matched with gaps found between particles forming the complementary rough face edge. Consequently the particles on both faces can be derived from a single continuous layer, corresponding to the ad-cytoplasmic component of the disk membrane. This observation seems to agree with a prevailing disk-membrane model in which the visual pigment molecules are localized in the ad-cytoplasmic lipid lamella, but not to conform with a recent hypothesis, based upon single replicas, that the fracture plane might pass along either the inner or outer true surface of the membrane and the visual pigment molecules be attached to the latter.