Role of actin filament organization in cell volume and ion channel regulation

Abstract

The actin cytoskeleton is an intracellular structure, which is involved in the onset and control of cell shape and function. In order for this relevant network to control its own and thus cell volume, specific interactions between the actin cytoskeleton and ion channel regulation controlling intracellular salt and water homeostasis may be invoked. The hypotonic shock‐induced, cell volume regulatory decrease (RVD) of most eukaryotic cells is a particularly useful example, as it is initiated and regulated by concerted processes involving both adaptive changes in actin filament organization and bulk fluid extrusion triggered by saline movement and the consequent decrease in cell water. The onset of RVD is linked to the selective activation of osmotically‐sensitive ion channels and other relevant ion transport mechanisms involved in the net ionic movement from the cytosol. Such regulatory processes, entailing effector changes in actin filament organization which target the plasma membrane, are largely unknown. In this report, recent studies are summarized implicating dynamic changes in gel properties of the actin cytoskeleton as the effector mechanism in the regulation of ion channel activity, and thus cell volume, in human melanoma cells. Based on the characterization of the hypotonic cell volume regulatory response of human melanoma cells devoid of a functional actin‐binding protein (ABP‐280, a filamin homolog) and their genetically rescued counterpart transfected with a functional ABP, a hypothesis is raised which is consistent with a regulatory “sensory” mechanism based on the ability of actin networks to respond to changes in the intracellular water‐salt homeostasis, which in turn effects signals controlling membrane function, including ion channel activity. J. Exp. Zool. 279:425–435, 1997. © 1997 Wiley‐Liss, Inc.

Rheology at the micro-scale: new tools for bio-analysis

“…The osmotic shock causes a rapid swelling of the cells, followed by a partial recovery of the cells' volume. These results are in good agreement with those reported in literature 33 .…”

“…The data of Figure 3 also shows that, after an initial swelling, the cells contract to a still swollen state that is ∼5% larger than when they were in isotonic media. Based on these observations, which are in close agreement with those already existing in literature 33 , we assume that these small radius changes do not affect the dynamics of the system appreciably, as discussed in the next section.…”

Osmo-Sensitive and Stretch-Activated Calcium-Permeable Channels in Vicia faba Guard Cells Are Regulated by Actin Dynamics

“…It is established that in animal cells, as a signal transducer, dynamic structural changes in actin microfilaments contribute to several signaling processes involving regulation of ion channel activities (Schwiebert et al, 1994;Cantiello, 1997;for review, see Janmey, 1998). In plants, it has become evident that actin microfilaments also function in signal transduction networks (for review, see Volkmann and Baluška, 1999).…”

Filamin Interacts with Epithelial Sodium Channel and Inhibits Its Channel Function

“…They are implicated in cell shape, motility, signal transduction, vesicular trafficking, and function of ion channel/transporter/receptor. The actin-based cytoskeleton has been shown to interact indirectly and directly with ion channels and membrane transport proteins (33)(34)(35). The hypothesis that actin cytoskeleton is directly involved in regulation of ENaC was first supported by a immunocolocalization study showing ENaC channels always present in close proximity to actin filaments and further demonstrated by characterizing the modulatory role of actin filament organization on ENaC channel activity in A6 epithelial cells (18).…”