Osmotic shrinkage of
Ehrlich ascites tumor cells (EATC) elicited translocation of
myosin II from the cytosol to the cortical region, and swelling elicits concentration of
myosin II in the Golgi region.
Rho kinase and p38 both appeared to be involved in shrinkage-induced
myosin II reorganization. In contrast, the previously reported shrinkage-induced actin polymerization [Pedersen et al. (1999) Exp. Cell Res. 252, 63-74] was independent of
Rho kinase, p38,
myosin light chain kinase (MLCK), and
protein kinase C (PKC), which thus do not exert their effects on the shrinkage-activated transporters via effects on
F-actin. The subsequent
F-actin depolymerization, however, appeared MLCK- and PKC-dependent, and the initial swelling-induced
F-actin depolymerization was MLCK-dependent; both effects were apparently secondary to
kinase-mediated effects on cell volume changes. NHE1 in EATC is activated both by osmotic shrinkage and by the
serine/threonine phosphatase inhibitor
Calyculin A (CL-A). Both stimuli caused
Rho kinase-dependent
myosin II relocation to the cortical cytoplasm, but in contrast to the shrinkage-induced
F-actin polymerization, CL-A treatment elicited a slight
F-actin depolymerization. Moreover,
Rho kinase inhibition did not significantly affect NHE1 activation, neither by shrinkage nor by CL-A. Implications for the possible interrelationship between changes in
F-actin and
myosin II,
protein phosphorylation, and cell volume regulation are discussed.