Up until 1960, no high resolution imagery of the Outer Segment of the photoreceptor cell of animal vision was available. Light microscopy had not been able to resolve the Outer Segment in sufficient detail to determine the character of any material surrounding the disks forming the majority of the Outer Segment. Conventional wisdom up to that time was that the Outer Segment was an integral part of the photoreceptor cell. However, authors frequently described the area surrounding the disks as the “zonulae adherentes” (Ohman, P. (1976) Fine structure of photoreceptors ... Vision Res. vol. 16, pp. 659-662)
During the 1960's, Brown, Gibbons & Wald (1963) and Young (shown in Rodieck 1973) provided a series of caricatures of the photoreceptor cell of mammals including the Outer Segment. These caricatures illustrated certain structural possibilities based on the assumption that the Outer Segment was enclosed by a biological membrane. However, they did not address other possibilities nor were they supported by factual data such as a high resolution micrograph. Hogan (1971) provided an electron micrograph at X36,000 that showed the disks exiting what could be a cup. The disk stack is shown surrounded by only a single unresolved, and possibly discontinuous, layer beyond this extrusion cup of the photoreceptor cell. Photomicrographs at X144,000 by Nilsson (1965) probably guided Young's thinking but they are inconclusive since the location of the photo micrograph was not specified precisely.[REF. 4.3]
A large number of subsequent electron micrographs, at magnifications greater than X150,000, have shown the Outer Segments to exhibit “extrusion marks” similar to those found on a bullet fired from a rifled barrel(Bownds & Brodie, J. Gen. Physiol. vol. 66, pp. 407-425 (1975). The marks are clearly thicker than a nominal membrane surrounding the Outer Segment. It is not clear such marks are compatible with an extremely thin membrane covering the surface of the Outer Segment. When these Outer Segments are broken, there is no sign of any debris associated with a membrane surrounding the segment. On the contrary, the broken ends are well defined and expose the detailed structure of the last remaining disk. [Ref. 4.6]
Nilsson proceeded to obtain very high resolution electron micrographs of individual disks that demonstrated that these disks were bilayer in construction and could be described as a bilayer (but not a plasma or biological) membrane. However, he did not present similar evidence for the putative membrane surrounding the disk stack.
Recently Molday has provided excellent micrographs of frog that show no plasma membranes between two disk stacks in frog. (Molday in Ogden, T. & Hinton, D. ed. (2001) Retina, 3rd Ed. Vol. 1, St. Louis, MO: Mosby pg 124) If each stack was enclosed by a plasma membrane, two plasma membranes should be easily recognized in these electron micrographs.
Two recent theories of transduction are entirely dependent on the existence of a biological membrane surrounding the disk stack of the Outer Segment. Both the calcium gate and the glutamate cascade theories depend on gates in the biological membrane surrounding the disk stack of the Outer Segment. Without a surrounding membrane, neither of these theories is viable. No definitive record could be found in the vision literature substantiating the existence of such a biological membrane enclosing the portion of the Outer Segment extending from the end of the inner segment of the photoreceptor cell and the beginning of the phagocytosis region associated with the retinal pigment epithelium (RPE) cells.
A REWARD of $1000 cash is being offered to the first group to provide an electron micrograph of a biological membrane (consisting of two recognizable bileaves) clearly definable as being that of a plasma membrane surrounding the disk stack of an Outer Segment in any mammal. The proof should consist of two relatable electron micrographs at different resolutions. The higher resolution micrograph should establish the existence of a double layer biological membrane surrounding the disk stack. The lower resolution micrograph should establish the fact that the higher resolution micrograph was obtained at a location distinctly separate from the tissue associated with the Inner Segment of a photoreceptor cell or the phagocytotic site of a retinal pigment epithelial cells. As a guide, the location should be at least 20 microns from either of the above structures. The lower resolution micrograph should be marked with an arrow, such as shown in Ohman as referenced above, or a box indicating the location included within the higher resolution micrograph. The same information relative to the gross location and shape of the membrane should appear in both micrographs.
There is no time limit on this REWARD offer.
The reward may be claimed by contacting
VISION CONCEPTS concerning the above evidence or by writing to:
Attn: James T. Fulton
1106 Sandpiper Dr.
Corona Del Mar, California, USA 92625-1407
The evidence supporting a claim for this reward shall become the property of the sponsor of the reward.