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THE EFFECT OF SALT CONCENTRATION OF THE MEDIUM ON THE RATE OF OSMOSIS OF WATER THROUGH THE MEMBRANE OF LIVING CELLS
1Laboratory of Pathology, School of Medicine, University of Pennsylvania Philadelphia, and the Marine Biological Laboratory, Woods Hole.
The Journal of General Physiology
|October 30, 2009
Summary
Sea urchin egg cells show increased water permeability in concentrated solutions. This suggests cell membranes expand in high osmotic pressure, facilitating faster water diffusion.
Area of Science:
- Cell biology
- Biophysics
- Osmosis
Background:
- Understanding cell membrane permeability is crucial for cell function.
- Osmotic pressure significantly influences water movement across cell membranes.
Purpose of the Study:
- To investigate the relationship between external osmotic pressure and the rate of water transport across the sea urchin egg cell membrane.
- To elucidate the mechanism of water permeability variation in response to osmotic gradients.
Main Methods:
- Utilized unfertilized sea urchin (Arbacia) eggs as osmometers.
- Measured the velocity constant of water diffusion across the cell membrane at varying external osmotic pressures.
- Plotted velocity constants against medium concentration to analyze the relationship.
Main Results:
- Water influx/efflux rate is dependent on the medium's osmotic pressure.
- Velocity constants for water diffusion were significantly higher in concentrated seawater and lower in diluted seawater.
- A tenfold difference in velocity constants was observed.
- Plotting velocity constants against medium concentration yielded a sigmoid curve.
Conclusions:
- Cell membrane water permeability increases with higher external osmotic pressure.
- This phenomenon can be explained by a model where the cell membrane, a hydrated gel, shrinks and widens its pores in concentrated solutions, enhancing water diffusion.
- Conversely, in less concentrated solutions, the gel hydrates, narrows pores, and reduces water permeability.
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