Membrane retrieval in non-exocytic and exocytic rat peritoneal mast cells

Mast cells were incubated with the membrane marker cationized ferritin (CF) in order to study the fate of cell membrane in both non-exocytic and in exocytic cells. Non-exocytic mast cells took up CF by a macropinocytic process by fusion of microfolds. CF particles occurred in lysosomal-like structures, in mast cell granules, and eventually in Golgi vesicles. Exocytic cells took up CF mainly by micropinocytosis and after 2 h CF appeared in Golgi vesicles and in progranules. The different uptake routes of CF in non-exocytic and in exocytic mast cells probably reflect that the former cells constantly take up material by macropinocytosis, perhaps for nutrition. The latter cells undergo a process of exocytosis-endocytosis in order to re-use retrieved surface membrane in new granule formation and in order to regain their ordinary size, which is greatly increased upon secretion.