Renal corpuscle of the African lungfish Protopterus dolloi:: Structural and histochemical modifications during aestivation

This work studies the structural and lectin-binding modifications experienced by the renal corpuscle of the African lungfish Protopterus dolloi during aestivation. The kidney of the aestivating animals was studied by light- and electron-microscopy,. and by immunofluorescence methods. Upon aestivation, the renal corpuscles (RCs) undergo a marked size reduction, and all the structural RC components are affected. The parietal cells of Bowman's capsule lose their flattened appearance and adopt the organization of a stratified epithelium. The glomerular capillaries collapse. The podocytes approach each other. Concomitantly, the major processes between contiguous cells are lost, the rest of the major processes adopting a lamina-like configuration. The foot processes lose their regular arrangement, the filtration slits are difficult to observe, and the subpodocyte space disappears. The glomerular basement membrane (GBM) thickens enormously, increases the amount of amorphous material and of collagen, and round inclusions formed by amorphous material and coiled fibrils appear. The mesangial cells compact and form a dense network embedded in the subendothelial lamina of the GBM. The endothelial cells show numerous irregularities, establishing abnormal interrelationships with the mesangial cells. These modifications are accompanied by changes in the expression of the carbohydrate moieties, as indicated by the modifications in lectin-binding patterns. On the whole, these modifications thicken and compact the filtration barrier, thus reducing the filtration coefficient and allowing the organism to cope with dehydration. All these modifications are partially reversed during the first days of returning the animals to freshwater. he renal corpuscle appears to be a highly dynamic structure capable of modifying its architecture in response to environmental changes.