Springer Online Journal Archives 1860-2000
Summary The renal corpuscles, juxtaglomerular cells, nephronic tubules, and ureters of female sticklebacks were studied. In fresh water fishes, the diameter of the renal corpuscles is similar to that found in fishes obtained from the sea, whereas the diameter of the glomeruli and the nuclei of the podocytes are slightly larger. Furthermore, in fresh water the podocytes produce secretory globules, which show some of the histochemical characteristics of the substance constituting the glomerular basement membrane. In sea water animals, secretory phenomena are absent. Mesangial cells, which are scarce in fresh water fishes, are numerous in marine animals. Similarly, juxtaglomerular cells, hard to find in fresh water fishes, are prominent in specimens from the sea. The development of the epithelia of the nephronic tubules and of the ureters is better in fresh water. The cells and the nuclei are larger. In the first proximal tubule, which is involved in the reabsorption and the digestion—by lysosomes—of macromolecules, “micropinocytosis vermiformis” occurs. The results of stereological analysis of the fractional volume of the mitochondria and of the relative extent of the infoldings of the basal cell membranes—the location of the ion transport mechanisms—in the three different segments of the nephronic tubule and in the ureter, point to the existence of a structural gradient along the kidney tubules. In fresh water fishes the mitochondrial volume, per surface unit of basal cell membrane, is low in the first proximal segment and is increasingly higher in the other segments, while the highest value is found in the ureter. This structural gradient may be functionally linked with osmotic and ionic gradients, which exist in the renal tubules in fresh water. In the kidney tubules of marine sticklebacks, which do not show a major osmotic gradient, the structural gradient is small. The results are discussed on the basis of the known physiological differences in the function of the kidney of euryhaline teleosts in fresh water and in the sea.
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