The osmotic effects of electron microscope fixatives

Area of Science:

• Biophysics
• Cell Biology
• Ichthyology

Background:

• Fish scales of sprat and herring possess reflecting cells with ordered guanine crystals.
• Crystal spacing in these cells dictates reflected light wavelengths, enabling direct observation of cell volume changes via color shifts.

Purpose of the Study:

• To investigate the effects of different fixation methods on the osmotic activity and volume regulation of fish scale reflecting cells.
• To determine if aldehyde fixation preserves or alters cellular osmotic properties.

Main Methods:

• Utilizing the color-changing property of fish scales as a direct indicator of cell volume changes.
• Comparing the osmotic responses of scale reflecting cells after fixation with osmium tetroxide versus aldehyde solutions in varying salt and sucrose concentrations.

Main Results:

• Osmium tetroxide fixation was found to abolish osmotic activity in the reflecting cells.
• Aldehyde fixation did not destroy osmotic activity and prevented volume changes when applied in iso-osmotic solutions (approx. 60% of physiological osmolarity).
• Post-aldehyde fixation, cells exhibited osmotic activity but reached equilibrium volumes in solutions with 60% lower concentrations than pre-fixation.

Conclusions:

• Aldehyde fixation preserves the osmotic responsiveness of fish scale reflecting cells, albeit with altered equilibrium volumes.
• Osmium tetroxide fixation irreversibly damages the osmotic capabilities of these cells.
• The study discusses potential mechanisms for the shift in osmotic equilibrium following aldehyde fixation.