Intracellular Signalling Involved in Volume Regulatory Decrease

Abstract

The following volume-sensitive channels are characterized in Ehrlich ascites tumor cells (EATC), (i) a tamoxifen- and AA acid sensitive, outwardly rectifying small anion channel (I_Cl,vol) with low field anion selectivity (I^->Cl^-) and moderate depolarisation-induced inactivation, (ii) a separate DIDS- and niflumic acid-sensitive organic osmolyte/anion channel (OOC) transporting predominantly taurine, and (iii) a clofilium- and Ba²⁺-sensitive, voltage- and Ca²⁺-insensitive 5 pS K⁺ channel (I_K,vol), resistant to a range of K⁺ channel inhibitors including ChTX, clotrimazole, apamin, kaliotoxin, margatoxin, and TEA, and with a pH_o dependence reminiscent of the two-pore domain background K⁺ channels TASK. Cell swelling leads to an immediate and transient 3.3 fold increase in the rate of AA release resulting from activation of cPLA₂α, which is found to be translocated to the nucleus upon cell swelling (probably to the inner nuclear membrane), where it is phosphorylated and activated by a G-protein coupled process. AA is a precursor for LTC₄, which is transported out of the cell, where it is converted to LTD₄, which activates I_K,vol, and OOC, whereas I_Cl,vol is activated via a different pathway. In the absence of an increase in [Ca²⁺]_i, the unitary conductance, kinetics, and pharmacological profile are similar for I_K,vol and the K⁺-channels activated by LTD₄.Tyrosine phosphorylations are involved in the volume regulatory pathways and in defining the volume set-point. Tyrosin kinases appear to be involved in the signalling sequence leading to opening of the channels, and tyrosin phosphatases seem to be involved in closing of the channels. Finally a significant de-polymerization of F-actin is observed after cell swelling, the potential role of which in the volume regulatory mechanisms is under investigation.

Heat-evoked Activation of TRPV4 Channels in a HEK293 Cell Expression System and in Native Mouse Aorta Endothelial Cells

“…Such a mechanism has been discussed elsewhere (21). Cell swelling may activate PLA 2 thereby producing arachidonic acid or a downstream metabolite as a possible ligand (32)(33)(34). Indeed, we have recorded channel activation by arachidonic acid.…”

Cell swelling increases intracellular calcium in Necturuserythrocytes

“…The ability of animal cells to regulate their volume is a fundamental property common to a large number of cell types and has been extensively reviewed (Grinstein and Foskett, 1990;Hoffman, 2000;Land et al, 1998;Lewis and Donaldson, 1990;McCarty and O'Neil, 1992;Strange, 1994). Volume regulation is of importance in cells exposed to anisotonic extracellular conditions, as well as in cells where transport of solutes or pathophysiological conditions change intracellular osmolality (Land et al, 1998;Lang et al, 1998;McManus et al, 1995).…”

P2X4 Activation Modulates Volume-sensitive Outwardly Rectifying Chloride Channels in Rat Hepatoma Cells

“…More recently, we established in the same cell system that exogenous application of H 2 O 2 induced PLC␥1 phosphorylation in isotonic conditions. Also, we demonstrated that the activation of this phospholipase was found to be essential for H 2 ] i was found to have a profound impact on the half-time constant for VSOR Cl Ϫ current onset without affecting the activation and the steady-state amplitude of the current.…”

“…However, increasing evidence supports the notion that these channels participate in several other physiological processes, such as salt transport and metabolic stress, apoptosis, proliferation, migration, and cell cycle regulation (1)(2)(3)(4)(5). Furthermore, it has also been suggested that a failure in the activation of these channels upon cell swelling is involved in necrotic cell death (6).…”

“…Volume-sensitive outwardly rectifying (VSOR) 2 Cl Ϫ channels are ubiquitously expressed in most mammalian cells types playing a central role in maintaining normal cell volume. However, increasing evidence supports the notion that these channels participate in several other physiological processes, such as salt transport and metabolic stress, apoptosis, proliferation, migration, and cell cycle regulation (1)(2)(3)(4)(5).…”