Macromolecular crowding and volume perception in dog red cells

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Cell volume regulation is crucial for cellular homeostasis.
• Membrane transporters, such as the Na/H exchanger and [K-Cl] cotransporter, are key players in volume control.
• The precise trigger for these transporters' activation (cell volume vs. solute concentration) remains debated.

Purpose of the Study:

• To investigate whether changes in cell configuration or solute concentration/dilution primarily signal cell volume changes in dog red blood cells.
• To elucidate the regulatory mechanism of membrane transporters in response to cell volume shifts.

Main Methods:

• Preparation of resealed red blood cell ghosts with controlled surface area and internal solute concentration.
• Induction of cell shrinkage and swelling in intact cells and resealed ghosts.
• Monitoring of Na/H exchange and [K-Cl] cotransporter activity.
• Assessing the correlation between transporter activation and cytosolic protein concentration versus cell volume.

Main Results:

• Both intact cells and resealed ghosts showed Na/H exchange activation upon shrinkage.
• Transporter activation correlated strongly with cytosolic protein concentration, independent of cell volume.
• Albumin-loaded ghosts exhibited heightened sensitivity to shrinkage, suggesting protein concentration's role.
• Similar findings were observed for the swelling-activated [K-Cl] cotransporter.

Conclusions:

• Cell volume perception in dog red cells is primarily determined by changes in cytoplasmic protein concentration.
• Macromolecular crowding is proposed as the regulatory mechanism for kinases and phosphatases controlling membrane transporters during volume changes.
• This study reframes the understanding of cell volume mechanosensing in red blood cells.