Low-sodium environment induces adaptation in salamander diluting segments

Abstract

The urodele Ambystoma tigrinum adapts to a distilled water environment by decreasing renal sodium excretion, but the site and mechanism of renal adaptation is unknown. Isolated diluting segments of Ambystoma kidney were studied after a 2-wk exposure of the animals to either distilled or artificial pond ([Na] = 1.2 meq/l) water. Identification of diluting segments was confirmed by electron microscopy. Morphometric study revealed evidence of increased tubular diameter and cellular hypertrophy in the distilled water group. Na+-K+-ATPase activity was increased in tubules from the distilled water group compared with tubules from the pond water group; 40.2 +/- 6.9 vs. 21.7 +/- 4.3 nM ADP generated.min-1.mm tubule length-1, P less than 0.036. This alteration in ATPase activity was due to an increase in the number of pump units present on the basolateral membrane, since specific ouabain binding was also doubled in distilled water compound with pond water group tubules, 20.7 +/- 2.3 vs. 9.1 +/- 0.9 fmol/mm tubule length tubules, P less than 0.011. An increase in transepithelial potential difference of the diluting segment was noted in distilled water group tubules (19.5 +/- 1.4 mV) compared with tubules in the pond water group (13.2 +/- 1.8 mV), P less than 0.015. We conclude that distilled water adaptation is associated with specific diluting segment structural and functional alterations, which are probably linked to an increase in sodium transport rate.

Adenylate cyclase uncoupled β-adrenergic receptors in salamander proximal tubules

“…30 min-mm-I TL. Because salamander cells are considerably larger than those of the rabbit, we decided to normalize both results for tubular wall volume, a crude estimate of total cell volume contained between the luminal and basslateral tubule margins that assumes that all tubules are cylindrical and ignores basolateral infoldings (Morgunov et al 1989). This parameter was the only one available for both salamander (Maunsbach and Boulpaep 1984) and rabbit (Welling and Welling 1975) proximal tubules, although a more precise estimate of true cell volume would be preferable.…”

Renal water and solute excretion in the Atlantic stingray in fresh water

“…Mechanisms of urine dilution regarding euryhaline elasmobranchs are currently unknown (Lacy & Reale, 1995). Comparisons of Na + /K + ATPase expression, transepithelial potentials and osmotic gradients, tubular water permeability, and tubular morphology in and along the more distal segments of the euryhaline elasmobranch kidney tubule may distinguish functional and structural adaptations that maintain high C H 2 O and allow these elasmobranchs to exploit freshwater environments (Morgunov et al, 1989).…”