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Low-sodium environment induces adaptation in salamander diluting segments
N S Morgunov1, D J Hirsch, I G Mobbs
1Department of Physiology, Dalhousie University, Faculty of Medicine, Halifax, Nova Scotia, Canada.
The American Journal of Physiology
|February 1, 1989
Summary
The tiger salamander (Ambystoma tigrinum) kidney adapts to freshwater by increasing sodium transport in its diluting segments. This involves structural changes and more sodium-potassium pumps, enhancing survival in low-sodium environments.
Area of Science:
- Physiology
- Comparative Biology
- Renal Physiology
Background:
- The urodele Ambystoma tigrinum regulates sodium balance in freshwater.
- The specific kidney site and mechanism for renal adaptation to low-sodium environments remain unclear.
Purpose of the Study:
- To investigate the site and mechanism of renal adaptation in Ambystoma tigrinum exposed to distilled water.
- To determine if diluting segments are involved in sodium conservation.
Main Methods:
- Isolated diluting segments from Ambystoma kidney were studied after 2-week exposure to distilled or artificial pond water.
- Electron microscopy confirmed diluting segment identification.
- Morphometric analysis, Na+-K+-ATPase activity assays, and ouabain binding were performed.
Main Results:
- Distilled water exposure led to increased tubular diameter and cellular hypertrophy in diluting segments.
- Na+-K+-ATPase activity and basolateral membrane pump units (ouabain binding) significantly increased in distilled water-acclimated tubules.
- Transepithelial potential difference was elevated in diluting segments from the distilled water group.
Conclusions:
- Distilled water adaptation in Ambystoma tigrinum involves structural and functional alterations in the kidney's diluting segments.
- Increased Na+-K+-ATPase activity and number of pump units suggest enhanced sodium reabsorption capacity.
- These adaptations likely contribute to maintaining sodium balance in hypotonic freshwater environments.