Abstract
The nephrons of four species of teleosts were examined histologically and histochemically for enzymes.In the carp the epithelial cells on every segment were deeply interdigitated with adjacent cells.The epithelial cells seem to exhibit high sodium permeability.Na-K-ATPase activity was localized in the distal tubules.Active transport of sodium seems to take place in the distal tubules, whereas the first and second proximal tubules may passively absorb the sodium.The renal tubules of marine teleosts are probably permeable to water, because the epithelial cells showed the poor interdigitations.Macromolecular materials are expected to be absorbed in the 1st proximal tubules of the carp, a marine catfish, and the yellowtail, but not for a frogfish, because the segments of the former three fishes exhibited intense activity of acid phosphatase and had pinocytotic invaginations in their cell apex.Distribution of carbonic anhydrase in the 1st and 2nd proximal tubules of the carp and yellowtail indicates that the secretion of hydrogen ion is performed in the 1st and 2nd proximal tubules.In the marine catfish, on the other hand, the distal tubules are expected to secrete the hydrogen ion from the localization of carbonic anhydrase in these regions.
