IDENTIFICATION OF CONE CLASSES IN XENOPUS RETINA BY IMMUNOCYTOCHEMISTRY AND STAINING WITH LECTINS AND VITAL DYES

The aim of the present study was to determine the number of cone class es in the Xenopus retina. We examined the dimensions and staining prop erties of cones, utilizing two monoclonal antibodies, COS-l and OS-2, developed by Szel and Rohlich (1985). Living cones also were reacted w ith the plant lectins peanut agglutinin (PNA) and wheat germ agglutini n (WGA) and with a fluorescent stilbene dye, DIDS, which binds selecti vely to red-sensitive cones (Kleinschmidt, 1991; Kleinschmidt and Haro si, 1999a,b). Three cone populations were distinguished based on diffe rences in size and staining properties. Eighty-eight percent of all co nes were stained strongly by COS-1, PNA, and DIDS, but weakly by OS-2. The group of cones stained by COS-1 had the largest mean dimensions o f outer segment length, width, and oil droplet diameter. COS-1 negativ e cones were divisible into two groups: a subclass of miniature cones (approximately 4% total cones) was stained strongly by OS-2, PNA, and DIDS. The balance, constituting approximately 9% total cones, were of intermediate size, were not stained by PNA and reacted weakly to OS-2 and DIDS. WGA stained all cones. Large, COS-1+ cones appear to be red- sensitive and belong to the class of anion-tunable cone pigments. We s uggest that the intermediate size, COS-1 negative cones are blue-sensi tive based on the finding that blue-sensitive chromatic horizontal cel ls connect to them preferentially (Witkovsky et al., work in progress) . The remaining class of miniature cones may be UV-sensitive, since an other amphibian, the salamander, has been shown to possess red-, blue- , and UV-sensitive cones (Ferry and McNaughton, 1991).