Pattern recognition of amino acid signals partitions the cells of the goldfish retina into nine statistically unique biochemical theme classes and permits a first-order chemical mapping of virtually all cellular space. Photoreceptors, bipolar cells, and ganglion cells display a set of unique, nominally glutamatergic type E1, E1+E2, and E4 signatures, respectively. All horizontal cells are assignable to a GABAergic gamma 2 class or a non-GABAergic class with a glutamate-rich E3 signature. The amacrine cell layer is largely a mixture of (1) a taurine-dominated T1 Muller's cell signature and (2) GABAergic gamma 1, glycinergic G1, and dual glycinergic/GABAergic G gamma 1 amacrine cell signatures. Several major conclusions emerge from this work. (1) Glutamatergic, GABAergic, and glycinergic neural signatures and glial signatures account for over 99% of the cellular space in the retina. (2) All known neurons in the goldfish retina are associated with a set of conventional nonpeptide neurotransmitters. (3) Multiple forms of metabolic profiles are associated with a single nominal neurotransmitter category. (4) Glutamate and aspartate contents exhibit overlapping distributions and are not adequate univariate probes for identifying cell classes. (5) Signatures can serve as quantitative measures of cell state.

Isolated frog retinas were incubated in vitro with a 4-h pulse of [3H]leucine, then chased for 32 h with a nonradioactive amino acid mixture. At the end of the incubation, light and electron microscope autoradiograms were prepared from some of the retinas. The autoradiograms revealed: (a) intense radioactivity in the basal disks of the rod outer segments, (b) diffuse label evenly distributed throughout the rod outer segments, and (c) a high concentration of label in the entire rod outer segment plasma membrane. Incubation under identical conditions, but with puromycin added, significantly inhibited the labeling of all of these components. To identify the labeled proteins, purified outer segments from the remaining retinas were analyzed biochemically by SDS disc gel electrophoresis and gel filtration chromatography. SDS gel electrophoresis showed that about 90% of the total rod outer segment radioactivity chromatographed coincident with visual pigment, suggesting that the radiolabeled protein in the plasma membrane is visual pigment. Gel filtration chromatography demonstrated that the radiolabeled protein co-chromatographed with rhodopsin rather than opsin, and that the newly synthesized visual pigment in both the basal disks and the plasma membrane is present in the native configuration.The outer segments of vertebrate photoreceptors contain stacks of hundreds of membranous disks bounded by a plasma membrane (Fig. I). In the rod outer segment (ROS) these disks are separated, closed sacs throughout the outer segment, except at the base where the first few consist of continuous infotdings of the plasma membrane (10, 11). The disks in the rod are constantly renewed throughout the life of the animal, with new ones being formed at the base of the ROS from proteins and lipids synthesized in the inner segment (32,33,35). This process displaces the older disks toward the apex of the outer segment, where small packages of them are shed, then phagocytized and digested by the pigment epithelium. The ROS is thus maintained at a relatively uniform length (34).The composition of ROS disk membranes has been well characterized. They consist of about 50% protein and 50% lipid with the visual pigment glycoprotein, rhodopsin, z comprising 80 90% of the total protein present in the disk (19,20,29). The lipid composition of the ROS is primarily phospholipid, and it has been shown that the t The terms rhodopsin and opsin are used to describe visual pigment in its native and bleached state, respectively. The more general term, visual pigment, is used when the bleaching state of the protein is not known. The interactions of visual pigment protein and its vitamin A chromophore are described by the following:

We have explored the use of the Na+-H+ ionophore monensin as a potential tool for the investigation of membrane assembly and transport in retinal photoreceptors. Autoradiographic analysis of frog retinas incubated with [3H]leucine in the presence of monensin revealed a lack of concentrated silver grains ("bands") at the base of the rod outer segments, in contrast to controls. This is indicative of a pronounced monensin-induced decrease in disc membrane assembly. Biochemical analyses of whole retinas and isolated rod outer segment membranes showed that protein synthesis (including opsin synthesis) was not significantly inhibited under these conditions, whereas passage of membrane protein to the rod outer segment was blocked. Glycerolipid synthesis was not significantly affected by monensin. The results suggest that membrane proteins (e.g., opsin) destined for incorporation into the rod outer segment must pass through the Golgi apparatus and demonstrate the potential utility of monensin for inhibiting aspects of marcomolecule transport in photoreceptors.