This recent paper in Cell describes a cancer cell using osmotic pressure to move in confined spaces. The cell preferentially inserts Na+/H+ antiporters in the leading membrane. I want someone to double-check my osmosis before I make students reason it out:
- The normal Na+/K+ pumps cause an increase in Na+ ions outside the cell, but little change in osmotic pressure across the membrane.
- Increased Na+/H+ antiporters will allow Na+ in while pushing H+ out at the "front" end of the traveling cell.
- While this causes little net solute change, it increases water flow into the cell via aquaporins (?? this part I find mysterious)
- Na+ continues to be pumped out of the cell by the Na+/K+ pump at the "back" end of the cell
- Water follows the Na+ through aquaporins out the "back" of the cell, moving the cell forward
I don't feel convinced that moving ions around like this is causing osmotic gradients. Can anyone convince me?