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Changes in ionic selectivity with changes in density of water in gels and cells
1Department of Medicine, School of Medicine, University of Auckland, Auckland, New Zealand.
Biophysical Journal
|May 12, 2009
Summary
Gels under osmotic stress exhibit altered water activity and density, influencing ion selectivity. This suggests a spectrum of water structures impacting cellular processes, potentially regulated by the sodium pump.
Area of Science:
- Physical Chemistry
- Biophysics
- Materials Science
Background:
- Gels in aqueous solutions reach steady states where water activity within the gel can differ from the external solution.
- Osmotic stress influences the physical properties of water within gel matrices.
Purpose of the Study:
- To investigate the relationship between water activity, molar volume, and ion selectivity in gels under osmotic stress.
- To explore the concept of a continuous spectrum of water structures and their properties.
Main Methods:
- Equilibration of gels with aqueous solutions of impermeant solutes.
- Measurement of water activity and density within the gel pores.
- Observation of ion selectivity (K+ vs. Na+) based on water activity.
Main Results:
- Water activity in gel pores was higher than in the external solution at steady state without pressure difference.
- Gel water density decreased to 0.96 with increasing osmotic stress.
- Gel water exhibited K+ selectivity when its activity was higher than external water, and Na+ selectivity when lower.
Conclusions:
- Water equilibrates between compartments of unequal osmolality by adjusting its molar volume.
- A spectrum of water structures exists, ranging from dense to expanded, influencing ion binding.
- These findings offer insights into the state of cytoplasmic water and its regulation by the sodium pump.
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