INVESTIGATIONS OF RECEPTOR-MEDIATED PHAGOCYTOSIS BY HORMONE-INDUCED (IMPRINTED) TETRAHYMENA-PYRIFORMIS

Receptor-mediated endocytosis by Tetrahvmena pyriformis was studied us ing tetramethylrhodamine isothiocyanate-labeled concanavalin A (TRTTC- Con A) with fluorescence and confocal microscopy. In the presence of i nsulin, or 24 h after insulin pretreatment (hormonal imprinting), the binding and uptake of TRITC-Con A increased when compared to controls, owing to the binding of TRITC-Con A to sugar oligomers of insulin rec eptors. Mannose inhibited the binding of Con A, thus demonstrating the specificity of binding. Histamine, a phagocytosis-promoting factor in mammals and Tetrahymena, and galactose, did not influence the uptake of TRITC-Con A.