UPTAKE AND INTRACELLULAR TRANSPORT PATHWAYS OF FLUORESCENT LIPID ANALOGUES IN AMOEBA PROTEUS (RHIZOPODA, AMOEBIDA)

摘要

The uptake and intracellular transport of 5 different lipid analogues derived from phosphatidylethanolamine, phosphatidyl choline, sphingomyelin, ceramide, and cholesterol have been studied in living Amoeba proteus using fluorescence microscopy. Phosphatidylcholine and sphingomyelin are predominantly transported from the external environment to the cell interior in a manner consistent with induced macropinocytosis. On the other hand, phosphatidylethanolamine, ceramide, and cholesterol mainly enter the cellular matrix by carrier-mediated, ATP-dependent transmembrane transport. In general, all lipid analogues are first imported to a large pool of endosomal or lysosomal vacuoles, and then partitioned to numerous tiny cisternal elements; only sphingomyelin remains in the lysosomes and is not exported to other membrane compartments. The ultrastructural localization of ceramide indicates that the cisternal elements result from the decay of the Golgi apparatus into single cisternae during lipid accumulation. As a whole, the transport pathway of lipid analogues in A. proteus from the cell surface to different cell organelles shows many similarities to respective processes in a variety of metazoan cells. [References: 32]