Regulation of an ATP‐conductive large‐conductance anion channel and swelling‐induced ATP release by arachidonic acid

Abstract

Mouse mammary C127 cells responded to hypotonic stimulation with activation of the volumedependent ATP-conductive large conductance (VDACL) anion channel and massive release of ATP. Arachidonic acid downregulated both VDACL currents and swelling-induced ATP release in the physiological concentration range with K d of 4-6 mM. The former effect observed in the wholecell or excised patch mode was more prominent than the latter effect observed in intact cells. The arachidonate effects were direct and not mediated by downstream metabolic products, as evidenced by their insensitivity to inhibitors of arachidonate-metabolizing oxygenases, and by the observation that they were mimicked by cis-unsaturated fatty acids, which are not substrates for oxygenases. A membrane-impermeable analogue, arachidonyl coenzyme A was effective only from the cytosolic side of membrane patches suggesting that the binding site is localized intracellularly. Non-charged arachidonate analogues as well as trans-unsaturated and saturated fatty acids had no effect on VDACL currents and ATP release, indicating the importance of arachidonate's negative charge and specific hydrocarbon chain conformation in the inhibitory effect. VDACL anion channels were inhibited by arachidonic acid in two different ways: channel shutdown (K d of 4-5 mM) and reduced unitary conductance (K d of 13-14 mM) without affecting voltage dependence of open probability. ATP 4_ -conducting inward currents measured in the presence of 100 mM ATP in the bath were reversibly inhibited by arachidonic acid. Thus, we conclude that swelling-induced ATP release and its putative pathway, the VDACL anion channel, are under a negative control by intracellular arachidonic acid signalling in mammary C127 cells.

ATP release from non-excitable cells

“…taurine) and the methylamine betaine [69]. Okada has presented evidence that the maxi anion conductance (VDAC-like-VDACL) is a plasma membrane ATP-conductive pore in mammary cancer cells [70] and in macula densa cells [44], and follow-up work shows that this conductance is inhibited by internal arachidonic acid [71]. VDAC is a mitochondrial ATPpermeable membrane pore, but has been suggested also to be present in the plasma membrane as a specific splice variant (pl-VDAC-1) [72].…”

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…In the immune system, the maxi-anion channel activity has been confirmed in B lymphocytes [98][99][100][101], in T lymphocytes [102][103][104] and in peritoneal macrophages [17,105]. In other tissues, mast cells [106], keratinocytes [107], osteogenic cells [108], cultured glomus cells of the carotid body [109], PC12 pheochromocytoma cells [110], pavement cells from the gills of the trout [111] and mammary gland C127 cells [8,11,112] have also been shown to possess this channel. Patch-clamping the intracellular organelles revealed the maxi-anion channel activity in sarcoplasmic reticulum ''sarcoballs'' [113], whereas the presence of this channel in endoplasmic reticulum [114] and in Golgi complex [115] was demonstrated by reconstituting these membranes into liposomes and lipid bilayers, respectively.…”

“…5) as well as DIDS and DPC [2,5,6,8,12,30,54,93,96,103,114]. However, maxi-anion channels were found to be completely insensitive to phloretin, which is a relatively specific blocker for VSOR [121], in mouse mammary C127 cells [8,112] and mouse astrocytes [5,6,8,112], and to glibenclamide (Fig. 5), which blocks not only CFTR but also VSOR [122], in mouse C127 cells [8], rat cardiomyocytes [2] and mouse astrocytes [5].…”

Human monocytes kill M-CSF-expressing glioma cells by BK channel activation

“…Cell swelling can be induced by monocyte/macrophagederived mediators such as H 2 O 2 (data not shown), 53 peroxynitrite, 54 arachidonic acid 55,56 and its metabolites, leukotrienes and prostaglandins. 57,58 In vivo there is evidence that inducible nitric oxide synthase and peroxynitrite are present at the subcutaneous mM-CSF tumor cell rejection sites.…”