GANGLIOSIDES IN ACETYLCHOLINE RECEPTOR-RICH MEMBRANES FROM TORPEDO-MARMORATA AND DISCOPYGE-TSCHUDII

The ganglioside composition of membranes enriched in nicotinic acetylc holine receptor (AChR) from the electric rays Discopyge tschudii and T orpedo marmorata has been determined, and compared to that of total el ectric organ. A ganglioside having the chromatographic mobility of GM2 constitutes the major ganglioside (almost-equal-to 60%) in total D. t schudii electric organ, followed by a component with the mobility of G D3 (almost-equal-to 10%), and a component running just below GD1a (abo ut 12%). Minor constituents running as GM3 (2%) and as polysialogangli osides (comprising 8-15%) were also observed. Purified native membrane s of D. tschudii and T. marmorata displayed a similar profile, except that they were richer in a GM1-like component, and the proportion of G M2-like gangliosides was lower than that in total electric organ. Usin g a I-125-cholera toxin overlay assay on neuraminidase-treated high-pe rformance thin layer chromatograms, the presence of GM1, GD1a and trac e amounts of GD1b and GT1 (or GQ) were detected in D. Tschudii total m embranes. Immunocytochemical trechniques showed the co-localization of gangliosides GQ1c/GT1c/GP1c, recognized by the monoclonal antibody Q2 11, and the AChR at the ventral, innervated face of the electrocyte.