LOW-TEMPERATURE REVERSIBLY INHIBITS TRANSPORT FROM TUBULAR ENDOSOMES TO A PERINUCLEAR, ACIDIC COMPARTMENT IN AFRICAN TRYPANOSOMES

We have used electron microscopy and flow cytofluorimetry to study end ocytosis and intracellular transport of fluid phase bovine serum album en gold complexes and membrane bound concanavalin A through endosomal compartments of bloodstream forms of Trypanosoma brucei rhodesiense. B oth markers were rapidly endocytosed from the flagellar pocket. Within 20 minutes at 37 degrees C the markers reached a large, vesicular, pe rinuclear compartment that stained heavily with the CB1 monoclonal ant ibody. Neither marker left the flagellar pocket and entered cells at 4 degrees C, When cells were incubated at 12 degrees C, both markers en tered the cell and were transported to collecting tubules, a tubular e ndosomal compartment that receives endocytosed material from coated en docytic vesicles. However, no material was transported from collecting tubules to the late,perinuclear compartment at 12 degrees C. The morp hology of collecting tubule membranes was specifically altered at 12 d egrees C; tubules became shorter and were arrayed near the flagellar p ocket. The morphological alteration and the block in transport of endo cytic markers to the perinuclear compartment seen at 12 degrees C were reversed 10 minutes after cells were returned to 37 degrees C. We als o used flow cytofluorimetric measurements of pH dependent fluorescence quenching to measure the pH of the terminal endocytic compartment. Fl uoresceinated lectins accumulated in a terminal compartment with a pH of 6.0-6.1, a value considerably higher than that of mammalian lysosom es, Fluorescence from fluoresceinated lectins in this terminal endocyt ic compartment was dequenched when blood-stream forms were incubated i n the presence of chloroquine.