Cell movement has been shown to require ion fluxes into and out of the cell (Schwab et al., Pflügers Arch 453, 421, 2007) as well as the expression of aquaporines in the cell membranes (Papadopoulus, Pflügers Arch 456, 693, 2008). It has thus been postulated that subcellular cell swellings accompany the dislocation of cell somata during migration. To investigate whether cellular volume changes occur in migrating oligodendrocyte precursor cells (OPCs) we investigated soma volume changes using scanning ion conductance microscopy (SICM).

SICMicroscopy is a technique to investigate the topography of soft non-conducting surfaces without mechanical contact (Hansma et al., Science 243, 641, 1989) by monitoring the distance between an electrolyte filled glass electrode tip and an insulator. In brief the method detects the surface of an insulator by detecting electrical resistance increases occuring when an electrode tip closely approaches an insulator submerged in conducting electrolyte solution. Our SICM (Happel et al., J. Microscopy 212, 144, 2003) allowed us to quantitatively monitor a surface of 30mm × 30mm with a lateral resolution of 1mm in a time of 10 minutes. Since the complete extension of living cells, including all processes, usually exceeds this area a mathematical method was developed to extract the part of the cell volume covered by the soma and to quantify the volume of the front and the rear part of the cell.

To investigate whether migration of cell somata is accompanied by volume changes here we measured velocities and volume changes of 33 oligodendrocyte precursor cells. Cell somata of accelerating cells increased their volumes by 11% 15% (n=9) prior to dislocation of cell body and nucleus whereas the cell soma volumes of the resting cells stayed constant (0% 5%; n=10). This swelling mainly is located at the cell front (accelerating cells: 15% 20%, resting cells: -3% 16%). Whereas a swelling of the front part preceded the movement of the nucleus the rear part moved almost synchronously with the nucleus.

Our observations support the concept that ion and water fluxes leading to local cell swelling play a prominent role in the dislocation of the nucleus during cell migration.