A mechanosensitive ion channel regulating cell volume (original) (raw)

Transient receptor potential channels in mechanosensing and cell volume regulation

Methods in enzymology, 2007

Transient receptor potential (TRP) channels are unique cellular sensors responding to a wide variety of extra- and intracellular signals, including mechanical and osmotic stress. In recent years, TRP channels from multiple subfamilies have been added to the list of mechano- and/or osmosensitive channels, and it is becoming increasingly apparent that Ca(2+) influx via TRP channels plays a crucial role in the response to mechanical and osmotic perturbations in a wide range of cell types. Although the events translating mechanical and osmotic stimuli into regulation of TRP channels are still incompletely understood, the specific mechanisms employed vary between different TRP isoforms, and probably include changes in the tension and/or curvature of the lipid bilayer, changes in the cortical cytoskeleton, and signaling events such as lipid metabolism and protein phosphorylation/dephosphorylation. This chapter describes candidate mechanosensitive channels from mammalian TRP subfamilies, d...

Swelling-activated ion channels: functional regulation in cell-swelling, proliferation and apoptosis

Acta Physiologica, 2006

Cell volume regulation is one of the most fundamental homeostatic mechanisms and essential for normal cellular function. At the same time, however, many physiological mechanisms are associated with regulatory changes in cell size meaning that the set point for cell volume regulation is under physiological control. Thus, cell volume is under a tight and dynamic control and abnormal cell volume regulation will ultimately lead to severe cellular dysfunction, including alterations in cell proliferation and cell death. This review describes the different swelling-activated ion channels that participate as key players in the maintenance of normal steady-state cell volume, with particular emphasis on the intracellular signalling pathways responsible for their regulation during hypotonic stress, cell proliferation and apoptosis.

Cell volume regulation and swelling-activated chloride channels

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2003

Maintenance of a constant volume is essential for normal cell function. Following cell swelling, as a consequence of reduction of extracellular osmolarity or increase of intracellular content of osmolytes, animal cells are able to restore their original volume by activation of potassium and chloride conductances. The loss of these ions, followed passively by water, is responsible for the homeostatic response called regulatory volume decrease (RVD). Activation of a chloride conductance upon cell swelling is a key step in RVD. Several proteins have been proposed as candidates for this chloride conductance. The status of the field is reviewed, with particular emphasis on ClC-3, a member of the ClC family which has been recently proposed as the chloride channel involved in cell volume regulation.

Intracellular ionic strength regulates the volume sensitivity of a swelling-activated anion channel

American Journal of Physiology-Cell Physiology, 1998

Cell swelling activates an outwardly rectifying anion channel termed VSOAC (volume-sensitive organic osmolyte/anion channel). Regulation of VSOAC by intracellular electrolytes was characterized in Chinese hamster ovary cells by whole cell patch clamp. Elevation of intracellular CsCl concentration from 40 to 180 mM resulted in a concentration-dependent decrease in channel activation. Activation of VSOAC was insensitive to the salt gradient across the plasma membrane, the intracellular concentration of specific anions or cations, and the total intracellular concentration of cations, anions, or electrolytes. Comparison of cells dialyzed with either CsCl or Na2SO4solutions demonstrated directly that VSOAC activation is modulated by intracellular ionic strength (μi). The relative cell volume at which VSOAC current activation was triggered, termed the channel volume set point, decreased with decreasing ionic strength. At μi = 0.04, VSOAC activation occurred spontaneously in shrunken cells...

The Role of Ion Channels in Cellular Mechanotransduction of Hydrostatic Pressure

Mechanically Gated Channels and their Regulation, 2012

Anthrax toxin protein receptor (ANTXR) 1 has many similarities to integrin and is regarded in some respects as a single-stranded integrin protein. However, it is not clear whether ANTXR1 responds to mechanical signals secondary to the activation of integrins or whether it is a completely new, independent and previously undiscovered mechanosensor that responds to an undefined subset of mechanical signaling molecules. Our study demonstrates that ANTXR1 is a novel mechanosensor on the cell membrane, acting independently from the classical mechanoreceptor molecule integrinβ1. We show that bone marrow stromal cells (BMSCs) respond to the hydrostatic pressure towards chondrogenic differentiation partly through the glycogen synthase kinase (GSK) 3β/β-Catenin signaling pathway, which can be partly regulated by ANTXR1 and might be related to the direct binding between ANTXR1 and low-density lipoprotein receptor-related protein (LRP) 5/6. In addition, ANTXR1 specifically activates Smad2 and upregulates Smad4 expression to facilitate the transport of activated Smad2 to the nucleus to regulate chondrogenesis, which might be related to the direct binding between ANTXR1 and Actin/Fascin1. We also demonstrate that ANTXR1 binds to some extent with integrinβ1, but this interaction does not affect the expression and function of either protein under pressure. Thus, we conclude that ANTXR1 plays a crucial role in BMSC mechanotransduction and controls specific signaling pathways that are distinct from those of integrin to influence the chondrogenic responses of BMSCs under hydrostatic pressure. Due to its limited blood supply and slow cellular metabolism, articular cartilage is difficult to repair following injury. Identifying methods for repairing defects in cartilage is an ongoing clinical problem 1-3. The biomechanical environment of articular cartilage can exert a devastating toll on neocartilage that lacks adequate biomechanical properties 4-7. Because stem cells have higher mechanical sensitivity than adult cells 8 , biomechanical signals may play key roles in regulating the phenotypic differentiation of stem cells 9. Stem cells can sense mechanical properties and perceive mechanical information that directs broad aspects of cell functions, including lineage commitment. Our previous work showed that stimulation with hydrostatic pressure could effectively activate the chondrogenic potential of BMSCs 10-13 , suggesting that stem cells pretreated with suitable mechanical stimulation could be transformed into "super cells" with high chondrogenic potential that could better survive the growth and secretion rhythm of residual stem cells surrounding a defect after implantation 14. However, although mechanical stimulation may be able to enhance the regeneration process of articular cartilage 15 , the underlying molecular regulation mechanism remains far from clear.

Evidence for the role of cell stiffness in modulation of volume-regulated anion channels

Acta Physiologica, 2006

Aim: To investigate the link between cell stiffness and volume-regulated anion current (VRAC) in aortic endothelium. Method: Bovine aortic endothelial cells (BAECs) were exposed to methylb-cyclodextrin (MbCD) to deplete cellular cholesterol and the changes in cellular stiffness were measured by micropipette aspiration. VRAC density was measured electrophysiologically in the same cell populations. Furthermore, to probe the effects of cholesterol depletion on the mechanics of 'deep' cytoskeleton, we employ a novel technique to analyse correlated motion of intracellular particles. Results: We show that cholesterol depletion results in cellular stiffening and an upregulation of VRAC density. Replenishing cellular sterol pool with epicholesterol, a chiral analogue of cholesterol, abrogates both of these effects. This indicates that cholesterol sensitivity of both cell mechanics and VRAC are due to changes in the physical properties of the membrane rather than due to specific sterol-protein interactions. We also show that cholesterol depletion increases the stiffness of the 'deep cytoskeleton' and that disruption of actin filaments abolishes both cell stiffening and upregulation of VRAC due to cholesterol depletion. Furthermore, comparing BAECs to human aortic endothelial cells (HAECs), we show that BAECs that are inherently stiffer also develop larger VRACs. Conclusions: Taken together, our observations suggest an increase in the cytoskeleton stiffness has a facilitatory effect on VRAC development. We suggest that stiffening of the cytoskeleton increases tension in the membranecytoskeleton layer and that in turn facilitates VRAC.

Pathophysiology and puzzles of the volume-sensitive outwardly rectifying anion channel

The Journal of Physiology, 2009

Cell swelling activates or upregulates a number of anion channels. Of the volume-activated or-regulated anion channels (VAACs or VRACs), the volume-sensitive outwardly rectifying anion channel (VSOR) is most prominently activated and ubiquitously expressed. This channel is known to be involved in a variety of physiological processes including cell volume regulation, cell proliferation, differentiation and cell migration as well as cell turnover involving apoptosis. Recent studies have shown that VSOR activity is also involved in a number of pathophysiological processes including the acquisition of cisplatin resistance by cancer cells, ischaemia-reperfusion-induced death of cardiomyocytes and hippocampal neurons, glial necrosis under lactacidosis as well as neuronal necrosis under excitotoxicity. Moreover, VSOR serves as the pathway for glutamate release from astrocytes under ischaemic conditions and when stimulated by bradykinin, an initial mediator of inflammation. So far, many signalling molecules including the EGF receptor, PI3K, Src, PLCγ and Rho/Rho kinase have been implicated in the regulation of VSOR activity. However, our pharmacological studies suggest that these signals are not essential components of the swelling-induced VSOR activation mechanism even though some of these signals may play permissive or modulatory roles. Molecular identification of VSOR is required to address the question of how cells sense volume expansion and activate VSOR.

Stretch-activated ion channels and membrane mechanics

Neuroscience Research Supplements, 1990

TRP channels of the transient receptor potential ion channel superfamily are involved in a wide variety of mechanosensory processes, including touch sensation, pain, blood pressure regulation, bone loading and detection of cerebrospinal fluid flow. However, in many instances it is unclear whether TRP channels are the primary transducers of mechanical force in these processes. In this study, we tested stretch activation of eleven TRP channels from six mammalian subfamilies. We found that these TRP channels were insensitive to short membrane stretches in cellular systems. Furthermore, we purified TRPC6 and demonstrated its insensitivity to stretch in liposomes, an artificial bilayer system free from cellular components. Additionally, we demonstrated that, when expressed in C. elegans neurons, mouse TRPC6 restores the mechanoresponse of a touch insensitive mutant but requires diacylglycerol for activation. These results strongly suggest that the mammalian members of the TRP ion channel family are insensitive to tension induced by cell membrane stretching and, thus, are more likely to be activated by cytoplasmic tethers or downstream components and to act as amplifiers of cellular mechanosensory signaling cascades.

Sensors and signal transduction pathways in vertebrate cell volume regulation

Contributions to nephrology, 2006

The ability to control cell volume is fundamental for proper cell function. This review highlights recent advances in the understanding of the complex sequences of events by which acute cell volume perturbation alters the activity of osmolyte transport proteins in cells from vertebrate organisms. After cell swelling, the main effectors in the process of regulatory volume decrease are swelling-activated K(+) and Cl(-) channels, a taurine efflux pathway, and KCl cotransport. After cell shrinkage, the main effectors in the process of regulatory volume increase are Na(+)/H(+) exchange, Na(+), K(+), 2Cl(-) cotransport, and in some cells, shrinkageactivated Na(+) channels. All of these proteins are regulated in a unique manner by cell volume perturbations. The molecular identity of most, although not all, of these transport pathways is now known. Among other important advances, this has lead to the identification of transporter binding partners such as protein kinases and phosphatases, cy...