ISSN:
1432-0878
Keywords:
Trophotaeniae
;
Endocytosis
;
Lysosomotropic bases
;
Ammonia
;
Chloroquine
;
Monensin
;
Xenotoca eiseni, Xenoophorus captivus (Teleostei)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The trophotaenial absorptive cells (TACs) in the goodeid teleosts, Xenotoca eiseni and Xenoophorus captivus facilitate macromolecular transport from mother to foetus. Various endocytic pathways operate in these cells as indicated by a highly compartmentalized vacuolar apparatus. A time-sequence analysis of the endocytotic activity involved in horseradish peroxidase (HRP) ingestion revealed that the solute marker was, for the most part, channelled to lysosome-like vacuoles. Alternatively, the electrostatic ligand cationized ferritin (CF) was also either transcytosed or regurgitated. In the TACs of Xenotoca eiseni, dose-dependent responses to ammonium ion (5 mM, 10mM, 20 mM), chloroquine (50 μM, 150 μM, 300 μM), and monensin (5 μM, 10 μM, 20 μM) were registered after incubation of embryos in HRP-saline supplemented with the respective reagents. Each drug produced qualitatively distinct structural alterations in the cell's vacuolar apparatus. Treatment with raising concentrations of NH4Cl caused progressive vacuolation. In a dose-related way, the chloroquine effect was reflected in the formation of a uniformly labelled labyrinthic membrane system, apparently a consequence of indiscriminate fusion events. Monensin-treated cells always had some densely labelled, lysosome-like vacuoles, but typical endosomes were for the most part missing. At higher concentrations of the ionophore, dense apical tubules progressively disintegrated. In the TACs of Xenoophorus captivus, CF-trafficking was traced in the presence of NH4Cl (10 mM), chloroquine (150 μM), or monensin (10 μM). Ammonia caused endosomal swelling and thus seemingly affected the lysosomal pathway, but recycling and transcytosis were qualitatively unaffected albeit at distinctly lower rates. After treatment with chloroquine, the ligand was uniformly distributed within a tubulo-lamellar membrane complex. Both recycling pathways and ligand processing pathways were probably blocked due to an indiscriminate fusion of vacuolar compartments. Monensin did not apparently inhibit lysosomal sequestration, but transcytotic vesicles were only rarely observed. A perturbation of the recycling mechanisms was indicated by the structural disintegration of many dense apical tubules.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00318450
