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Activation energy for water transport in toad bladder
The American Journal of Physiology
|January 1, 1983
Summary
Measurements of water movement activation energy across epithelia are unreliable due to rapid changes in membrane permeability. Stabilizing water channels with glutaraldehyde revealed activation energies similar to water
Area of Science:
- Physiology
- Biophysics
Background:
- Activation energies (Ea) for water transport across vasopressin (ADH)-sensitive epithelia are typically ~10 kcal/mol.
- Previous measurements of Ea for osmotic water flow are questioned due to temperature-induced membrane permeability changes.
Purpose of the Study:
- To investigate the reliability of Ea measurements for osmotic water flow across toad bladders.
- To determine the activation energy for water movement through stabilized ADH-induced channels.
Main Methods:
- Toad bladders were exposed to ADH, then fixed with glutaraldehyde to stabilize water channels.
- Osmotic gradients were applied across fixed bladders at various temperatures to measure water flow.
- Activation energies for water flow were compared to those for bulk water viscosity.
Main Results:
- Temperature changes rapidly alter membrane water permeability, making standard Ea measurements unreliable.
- Stabilized ADH-induced channels yielded Ea values of 5.1, 4.3, 3.6, and 3.6 kcal/mol across different temperature ranges.
- These Ea values closely correlated with the calculated Ea for bulk water viscosity.
Conclusions:
- Rapid turnover of water permeability sites occurs in ADH-sensitive epithelia.
- The close correlation suggests water movement through ADH channels involves breaking hydrogen bonds, similar to bulk water fluidity.