The Osmotic Migration of Cells in a Solute Gradient

Abstract

The effect of a nonuniform solute concentration on the osmotic transport of water through the boundaries of a simple model cell is investigated. A system of two ordinary differential equations is derived for the motion of a single cell in the limit of a fast solute diffusion, and an analytic solution is obtained for one special case. A two-dimensional finite element model has been developed to simulate the more general case (finite diffusion rates, solute gradient induced by a solidification front). It is shown that the cell moves to regions of lower solute concentration due to the uneven flux of water through the cell boundaries. This mechanism has apparently not been discussed previously. The magnitude of this effect is small for red blood cells, the case in which all of the relevant parameters are known. We show, however, that it increases with cell size and membrane permeability, so this effect could be important for larger cells. The finite element model presented should also have other applications in the study of the response of cells to an osmotic stress and for the interaction of cells and solidification fronts. Such investigations are of major relevance for the optimization of cryopreservation processes.

Involvement of aquaporin-4 in astroglial cell migration and glial scar formation

“…During migration through the pore, the front end of astroglia becomes exposed to the osmolality of the bottom chamber while the rear end is exposed to the osmolality of the top chamber. In agreement with previous findings (Anderson, 1983;Jaeger et al, 1999;Zinemanas and Nir, 1995), our experiments showed that the speed of astroglial cell migration can be altered by a small osmotic gradient in the extracellular medium, resulting in accelerated astroglia migration towards hypo-osmolality.…”

“…However, the idea that these water fluxes are primarily mediated by aquaporins is new (Saadoun et al, 2005). Theoretical calculations show that transmembrane water fluxes induced by small extracellular osmotic gradients can generate enough force to propel vesicles (Anderson, 1983;Zinemanas and Nir, 1995) and even cells (Jaeger et al, 1999) through extracellular solutions. During this process, termed osmophoresis, the vesicles/cells move towards hypo-osmolality as water enters into the front end and leaves from the rear end of the cell.…”

Aquaporins and cell migration

“…Theoretical calculations suggest that unequal rates of water entry into the front vs back portions of a cell (produced by placing a cell in an osmotic gradient) can generate enough force to propel a cell forward toward hypo-osmolality without the need for actin involvement [14]. Based on these observations, we suggest that AQP-mediated transmembrane water movements may play two important roles in the migration process: facilitate cell shape changes and help propel the cell forward.…”

Water flux in cell motility: Expanding the mechanisms of membrane protrusion

“…Accordingly it has been shown that heavy water induce cell shape changes and reduce motility of human neutrophils [Zimmermann et al, 1988]. Osmolality also affects tumor cell pseudopod protrusions [You et al, 1996], and theoretical analyses show that an osmotic gradient elicits water fluxes that promote movement of cells [Jaeger et al, 1999]. Moreover, fluxes of water can be examined using self-quenching of fluorophores [Hamann et al, 2002;Solenov et al, 2004], a method that also has been used to visualize water fluxes during neutrophil spreading and motility ( Fig.…”