Osmotic properties of human red cells

Area of Science:

• Physiology
• Biophysics
• Cell Biology

Background:

• Human red blood cells display anomalous volume changes when subjected to osmotic pressure gradients.
• Previous research suggested a concentration dependence of hemoglobin charge (ZHb) to explain these anomalies, but this has been difficult to replicate.
• A significant volume anomaly persists in red cells, even after considering known physical-chemical constraints.

Purpose of the Study:

• To investigate the persistent anomalous volume changes in human red blood cells under osmotic pressure.
• To re-evaluate the proposed concentration dependence of hemoglobin charge (ZHb).
• To identify potential causes for the observed anomalies in both shrunken and swollen red cells.

Main Methods:

• Replication of previous experimental findings regarding red cell volume changes.
• Analysis of osmotic pressure gradients and their effect on cell volume.
• Consideration of hemoglobin osmotic coefficients, ionic strength, and solute binding.

Main Results:

• The concentration dependence of hemoglobin charge (ZHb) proposed by Gary-Bobo and Solomon could not be confirmed.
• A significant anomaly of 12.5 +/- 0.8% of total isosmotic cell water remains unexplained by known factors.
• Anomalies in shrunken cells may relate to ionic strength dependence of the hemoglobin osmotic coefficient.
• In swollen cells, increased solute binding to proteins at low ionic strength may contribute to anomalous behavior.

Conclusions:

• The anomalous volume changes in human red blood cells cannot be fully explained by the colligative properties of hemoglobin or previously proposed ZHb effects.
• Ionic strength dependence of the hemoglobin osmotic coefficient in shrunken cells and increased solute binding in swollen cells are suggested as potential contributors to the observed anomalies.