Distribution of actin, actin-binding proteins, 43K protein, and spectrin in D. tschudii electrocytes

With a view to establishing the location of proteins related to the nicotinic cholinergic receptor (AChR), immunocytochemical studies were carried out in the electric tissue of the South American ray Discopyge tschudii. The receptor protein was localized at the innervated, ventral region of the electrocyte in cryostat sections using Texas Red-labelled alpha-bungarotoxin, a specific AChR marker. A series of antibodies against actin and actin-associated proteins (alpha-actinin, vinculin, tropomyosin and spectrin) were also employed in indirect immunofluorescence assays. Furthermore, with the aid of the monoclonal antibody 1234A, the peripheral, nonreceptor 43K protein was found to be colocated with the AChR and spectrin at the ventral surface of the electrocyte. NBD-phallacidin was used to detect the filamentous form of actin or F-actin. The anti-actin antibody recognized epitopes throughout the electrocyte cytoplasm. F-actin was mainly distributed at the dorsal, non-innervated region, where alpha-actinin, vinculin and tropomyosin were also localized. The results indicate a) the existence of a close structural relationship between the 43K protein, spectrin, and the AChR at the ventral, innervated face of the electrocyte; b) the occurrence of an actin isoform probably mono or oligomeric-throughout the electrocyte's cytoplasm, and c) the possible association of F-actin, localized at the dorsal region of the electrocyte, with alpha-actinin, tropomyosin and vinculin, as in other cellular systems.