Reversible conformational changes of plasmalemmal glycoproteins

Area of Science:

• Biochemistry
• Cell Biology
• Hematology

Background:

• Red blood cells exhibit unique behaviors in varying ionic environments.
• The erythrocyte surface, particularly the glycocalyx, plays a crucial role in cell interactions.

Purpose of the Study:

• To investigate the phenomenon of reversible red blood cell agglutination in low ionic media.
• To elucidate the underlying mechanisms, including ion dynamics and surface glycoprotein changes.

Main Methods:

• Incubation of human red blood cells in low ionic isotonic sucrose.
• Monitoring of agglutination and disagglutination.
• Measurement of extracellular ion concentrations (specifically K+).
• Treatment with KCL to observe agglutinate decomposition.
• Glutaraldehyde fixation and analysis of surface properties (staining, colloidal iron binding, electrophoretic velocity).

Main Results:

• Instantaneous agglutination of red blood cells occurred in low ionic sucrose.
• Complete disagglutination was observed within 60-90 minutes.
• Disagglutination correlated with a significant efflux of cellular ions, increasing extracellular K+ 500-fold.
• Addition of KCL rapidly reversed agglutination.
• Glutaraldehyde-fixed cells showed loss of anisotropic staining and colloidal iron binding, suggesting glycocalyx changes.
• Ruthenium red staining and electrophoretic velocity remained unchanged compared to controls.

Conclusions:

• The reversible agglutination and disagglutination of red blood cells in low ionic media are driven by ion fluxes.
• These observations provide evidence for the reversible unfolding of glycocalyx glycoproteins under low ionic stress.
• The erythrocyte glycocalyx exhibits dynamic conformational changes in response to environmental ionic strength.