The cytoskeleton and cell volume regulation.

Although the precise mechanisms have yet to be elucidated, early events in osmotic signal transduction may involve the clustering of cell surface receptors, initiating downstream signaling events such as assembly of focal adhesion complexes, and activation of, e.g. Rho family GTPases, phospholipases, lipid kinases, and tyrosine- and serine/threonine protein kinases. In the present paper, we briefly review recent evidence regarding the possible relation between such signaling events, the F-actin cytoskeleton, and volume-regulatory membrane transporters, focusing primarily on our own work in Ehrlich ascites tumer cells (EATC). In EATC, cell shrinkage is associated with an increase, and cell swelling with a decrease in F-actin content, respectively. The role of the F-actin cytoskeleton in cell volume regulation in various cell types has largely been investigated using cytochalasins to disrupt F-actin and highly varying effects have been reported. Findings in EATC show that the effect of cytochalasin treatment cannot always be assumed to be F-actin depolymerization, and that, moreover, there is no well-defined correlation between effects of cytochalasins on F-actin content and their effects on F-actin organization and cell morphology. At a concentration verified to depolymerize F-actin, cytochalasin B (CB), but not cytochalasin D (CD), inhibited the regulatory volume decrease (RVD) and regulatory volume increase (RVI) processes in EATC. This suggests that the effect of CB is related to an effect other than F-actin depolymerization, possibly its F-actin severing activity.