A low zinc diet leads to loss of Zn in melanosomes of the RPE but not in melanosomes of the choroidal melanocytes.
Long Evans rats were treated by a low-Zinc-Diet (ZD) and the ultrastructure and elemental composition of melanosomes of the RPE and choroidal melanocytes and RPE lipofuscin granules were investigated using Analytical Electron Microscopy (AEM). In controls the Zn mole fraction of melanosomes was 0.05 at% (RPE) and 0.06 at% (choroid), respectively. For ZD-rats the Zn mole fraction of these granules was almost unchanged in the choroid but decreased and was below the detection limit (0.02 at%) in the RPE. ZD-rats produced also giant melanosomes (diameter 1-3 μm) in the choroid and greatly increased amounts of RPE lipofuscin. The giant melanosomes contained about six times as much Cu as control melanosomes. Lipofuscin granules were identified by AEM and could be clearly distinguished from melanosomes by their chemical composition. Thus, changes of the ultrastructure and transition metal storage of melanosomes due to a ZD can be directly traced using AEM.
Institute of Applied Physics, University of Tuebingen, Auf der Morgenstelle 10, 72076 Tuebingen, Germany. antje.biesemeier@med.uni-tuebingen.de
Antje
A
Biesemeier
Sylvie
S
Julien
Despina
D
Kokkinou
Ulrich
U
Schraermeyer
Oliver
O
Eibl
D000818:Animals; D002829:Choroid / Q000737:chemistry / Q000166:cytology; D003300:Copper / Q000032:analysis; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure; D004032:Diet; D004577:Electron Probe Microanalysis; D008062:Lipofuscin / Q000378:metabolism; D008544:Melanocytes / Q000737:chemistry* / Q000648:ultrastructure; D020460:Melanosomes / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D051381:Rats; D020318:Rats, Long-Evans; D055213:Retinal Pigment Epithelium / Q000737:chemistry* / Q000648:ultrastructure; D046590:Spectroscopy, Electron Energy-Loss; D015032:Zinc / Q000032:analysis*
D008062:Lipofuscin; D003300:Copper; D015032:Zinc