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?
Since posting, I did some more research using background refs from the intro (who knew?). The trick seems to be that when protons are pumped out, the cell regenerates them from water in order to maintain pH. So the solute concentration DOES increase inside the cell with more Na/H transport.