Three-dimensional representation and quantification of endosomes in the rat kidney proximal tubule cell.
The organization of the endosomal compartment in the rat kidney proximal tubule cell was studied by computer-aided three-dimensional reconstruction based on tracing of serial thin sections. Besides the well-documented endocytic elements such as small vesicles, tubules and large vacuoles, the endosomal compartment contained a prominent structural complex consisting of a central vacuolar element (with diameters up to 2000 nm) and associated systems of radiating tubular profiles. The large endosomes examined had from two to twenty-four tubules as straight or bending extensions directed randomly from the central vacuole. The tubules were 70-90 nm in diameter and varied with the length up to 1500 nm. Quantitative evaluation from examples of the large endosomes with more than ten tubular extensions, showed that 25-40% of the membrane resided in the tubular portion in contrast to 5-10% of the volume. These results indicate the high efficiency of the role of the endosomal tubules as a mediator of the membrane recycling, because the tubules simultaneously allow retention of most of the content in the central vacuole during the recycling process.
Kawai
Y
Y
Department of Anatomy, Kagawa Medical School, Japan.
Hatae
T
T
D000818:Animals; D002451:Cell Compartmentation; D004705:Endocytosis; D007091:Image Processing, Computer-Assisted; D007687:Kidney Tubules, Proximal / Q000648:ultrastructure*; D008870:Microtubules / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains; D014617:Vacuoles / Q000648:ultrastructure*