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Biomedical subjects

I H Lambert

Publications and source records attributed to I H Lambert.

At least 19 recordsLinked to original sources
PubMed2001

Cellular model for induction of drip loss in meat.

Drip loss from porcine muscle (M. longissimus dorsi) contained high concentrations of K(+) ( approximately 135 mM) and organic osmolytes, for example, taurine ( approximately 15 mM), as well as significant amounts of protein ( approximately 125 mg.mL(-1)). Thus, the drip reflects release of intramuscular components. To simulate events taking place at the time of slaughter and leading to release of osmolytes and subsequent formation of drip loss, C2C12 myotubes were exposed to anoxia and reduction in pH (from 7.4 to 6.0). Anoxia and acidification increased the cellular Ca(2+) concentration ([Ca(2+)](i)) at a rate of 22-32 nM.min(-)(1). The anoxia-induced increase in [Ca(2+)](i) was mainly due to influx via sarcolemmal Na(+) channels. As mammalian cells swell and release lysophospholipids during anoxia, C2C12 cells and primary porcine muscle cells were exposed to either hypotonic shock or lysophosphatidylcholine (LPC) and the release of taurine was followed. The swelling-induced taurine efflux was blocked in the presence of the anion channel blocker (DIDS), the 5-lipooxygenase inhibitors (ETH 615-139 and NDGA) but unaffected by the presence of vitamin E. In contrast, the LPC-induced taurine release was unaffected by DIDS but abolished by antioxidants (butylated hydroxytoluene and vitamin E). Thus, stress-induced taurine release from muscles may precede by two different mechanisms, one being 5-lipooxygenase dependent and the other involving generation of reactive oxygen species. A model for the cellular events, preceding formation of drip in meat, is presented.

Animals↗
PubMed2000

Lysophosphatidylcholine induces taurine release from HeLa cells.

The putative role of lysophospholipids in activation and regulation of the volume-sensitive taurine efflux was investigated in HeLa cells using tracer technique. Lysophosphatidylcholine (LPC, 10 microm) with oleic acid increased taurine efflux during hypotonic and isotonic conditions. Substituting palmitic or stearic acid for oleic acid enhanced taurine release during isotonic conditions, whereas ethanolamine, serine or inositol containing lysophospholipids were ineffective. High concentrations of LPC (25 microm) induced Ca(2+) influx, loss of adenosine nucleotides, taurine and the Ca(2+)-sensitive probe Fura-2, and thus reflected a general breakdown of the membrane permeability barrier. Low concentrations of LPC (5-10 microm) solely induced taurine efflux. The LPC-induced taurine release was unaffected by anion channel blockers (DIDS, MK196) and the 5-lipoxygenase inhibitor ETH 615-139, which all blocked the volume sensitive taurine efflux. Furthermore, LPC-induced taurine release was reduced by antioxidants (NDGA, vitamin E) and the protein tyrosine kinase inhibitor genistein. The swelling-induced taurine efflux was in the absence of LPC unaffected by vitamin E, blocked by genistein, and increased by H(2)O(2) and the protein tyrosine phosphatase inhibitor vanadate. It is suggested that low concentrations of LPC permeabilizes the plasma membrane in a Ca(2+)-independent process that involves generation of reactive oxygen species and tyrosine phosphorylation, and that LPC is not a second messenger in activation of the volume sensitive taurine efflux in HeLa cells.

Antioxidants↗
PubMed2000

Cell shrinkage is essential in lysophosphatidic acid signaling in Ehrlich ascites tumor cells.

The present study aimed at elucidating the initial intracellular lysophosphatidic acid (LPA)-induced signaling events, in order to investigate the sequence in which LPA affects the intracellular concentration of free, cytosolic Ca(2+), [Ca(2+)](i), ion channels, the F-actin cytoskeleton, cell volume and the Na(+)/H(+) exchanger. We found that stimulation of Ehrlich cells with LPA induced a transient, concentration-dependent increase in [Ca(2+)](i), which is due to Ca(2+) release from intracellular Ins(1,4,5)P(3)-sensitive stores as well as an influx of Ca(2+). The EC(50) values for LPA-induced Ca(2+) mobilization were estimated at 0.03 nm and 0.4 nm LPA in the presence and absence of extracellular Ca(2+), respectively. The LPA-induced increase in [Ca(2+)](i) resulted in (i) co-activation of Ca(2+)-activated, charybdotoxin (ChTX)-sensitive K(+) and niflumic acid-sensitive Cl(-) currents; (ii) a subsequent cell shrinkage and increased polymerization of F-actin, and (iii) activation of a Na(+)/H(+) exchange, resulting in a concentration-dependent intracellular alkalinization. The EC(50) value for the LPA-induced rate of alkalinization was estimated at 0. 37 nm LPA. When cell shrinkage was prevented, the LPA-induced activation of the Na(+)/H(+) exchanger was impaired. In conclusion, the initial signaling events induced by LPA involves activation of volume regulatory mechanisms.

Actins↗
PubMed2000

Hypotonic cell swelling induces translocation of the alpha isoform of cytosolic phospholipase A2 but not the gamma isoform in Ehrlich ascites tumor cells.

We demonstrate that two isoforms of the cytosolic phospholipase A2, cPLA2alpha and cPLA2gamma, are present in Ehrlich ascites tumor cells. Both enzymes are almost uniformly distributed throughout the cells under control conditions, as visualized by laser-scanning confocal microscopy. Stimulation by either hypotonic cell swelling or addition of the Ca2+ ionophore A23187 results in translocation of cPLA2alpha, but not cPLA2gamma, to the nucleus, where it forms hot-spot-like clusters. Our group previously showed that release of radioactively labeled arachidonic acid, incorporated into the phospholipids of Ehrlich cells, was immediately and transiently increased on hypotonic cell swelling [Thoroed, S.M., Lauritzen, L., Lambert, I.H., Hansen, H.S. & Hoffmann, E.K. (1997) J. Membr. Biol. 160, 47-58]. We now demonstrate that arachidonic acid is released from the nuclear fraction following hypotonic exposure. Stimulation of Ehrlich cells with A23187 also leads to an increase in arachidonic acid release from the nucleus. However, as hypotonic cell swelling is not accompanied by any detectable increase in intracellular concentration of free cytosolic Ca2+ ([Ca2+]i), stimulus-induced translocation of cPLA2alpha can also occur without elevation of [Ca2+]i. The stimulus-induced translocation of cPLA2alpha appears not to be prevented by inhibition of mitogen-activated protein (MAP) kinase activation, p38 MAP kinase, tyrosine kinases and protein kinase C, hence, phosphorylation is not crucial for the stimulus-induced translocation of cPLA2alpha. Disruption of F-actin did not affect the translocation process, thus, an intact F-actin cytoskeleton does not seem to be required for translocation of cPLA2alpha.

Animals↗
PubMed1999

Mechanical stress induces release of ATP from Ehrlich ascites tumor cells.

The supernatant from a suspension of Ehrlich cells exposed to centrifugation at 700xg for 45 s induced a transient increase in the intracellular concentration of free, cytosolic Ca2+, [Ca2+]i, as well as activation of an outwardly rectifying whole-cell current when added to a suspension of non-stimulated cells. These effects were inhibited by suramin, a non-specific P2 receptor antagonist, and mimicked by ATP. Reversed phase HPLC analysis revealed that the supernatant from Ehrlich cells exposed to centrifugation contained 2. 6+/-0.2 microM ATP, and that the mechanical stress-induced release of ATP was inhibited by glibenclamide and verapamil, non-specific inhibitors of the cystic fibrosis transmembrane conductance regulator and P-glycoprotein, respectively. After trypan blue staining, less than 0.5% of the cells were unable to extrude the dye. Addition of extracellular ATP induced a suramin-sensitive, transient, concentration-dependent increase in [Ca2+]i, activation of an outwardly rectifying whole-cell current and a hyperpolarization of the plasma membrane. The ATP-induced hyperpolarization of the plasma membrane was strongly inhibited in the presence of charybdotoxin (ChTX), an inhibitor of several Ca2+-activated K+ channels, suggesting that stimulation of P2 receptors in Ehrlich cells evokes a Ca2+-activated K+ current. The relative potencies of several nucleotides (ATP, UTP, ADP, 2-MeSATP, alpha,beta-MeATP, bzATP) in eliciting an increase in [Ca2+]i, as well as the effect of repetitive addition of nucleotides were investigated. The results lead us to conclude that mechanical stimulation of Ehrlich cells leads to release of ATP, which in turn stimulates both P2Y1 and P2Y2 receptors, resulting in Ca2+ influx as well as release and activation of an outwardly rectifying whole-cell current.

Adenosine Triphosphate↗
PubMed1998

P2 receptor-mediated signal transduction in Ehrlich ascites tumor cells.

The mechanisms, by which the P2 receptor agonists adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP) evoke an increase in the free cytosolic calcium concentration ([Ca2+]i) and in intracellular pH (pHi), have been investigated in Ehrlich ascites tumor cells. The increase in [Ca2+]i evoked by ATP or UTP is abolished after depletion of intracellular Ca2+ stores with thapsigargin in Ca2+-free medium, and is inhibited by U73122, an inhibitor of phospholipase C (PLC), indicating that the increase in [Ca2+]i is primarily due to release from intracellular, Ins(1,4,5)P3-sensitive Ca2+ stores. ATP also activates a capacitative Ca2+-entry pathway. ATP as well as UTP evokes a biphasic change in pHi, consisting of an initial acidification followed by alkalinization. Suramin and 4,4'-diisothiocyano-2,2'-stilbene-disulfonic acid (DIDS) inhibit the biphasic change in pHi, apparently by acting as antagonists at P2 receptors. The alkalinization evoked by the P2 receptor agonists is found to be due to activation of a 5'-(N-ethyl-N-isopropyl)amiloride (EIPA)-sensitive Na+/H+ exchanger. ATP and UTP elicit rapid cell shrinkage, presumably due to activation of Ca2+ sensitive K+ and Cl- efflux pathways. Preventing cell shrinkage, either by incubating the cells at high extracellular K+ concentration, or by adding the K+-channel blocker, charybdotoxin, does not affect the increase in [Ca2+]i, but abolishes the activation of the Na+/H+ exchanger, indicating that activation of the Na+/H+ exchanger is secondary to the Ca2+-induced cell shrinkage.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Calyculin A modulates the kinetic constants for the Na+-coupled taurine transport in Ehrlich ascites tumour cells.

The effect of the phosphatase inhibitor calyculin A (cal A) on the kinetic parameters of the Na+-coupled taurine uptake via the taurine transporter in the Ehrlich ascites tumour cells has been investigated. Preincubation with cal A (100 nM) reduces the initial taurine influx by about 20%, but has no effect on the diffusional component of the taurine influx or on the taurine release from cells suspended in isotonic or in hypotonic medium. Thus, cal A-sensitive phosphatases only affect taurine transport mediated by the Na+-dependent taurine transporter. Cal A increases the Michaelis-Menten constant for binding of taurine to the transporter from 31+/-6 to 45+/-4 microM and reduces the taurine transport capacity from 210+/-20 to 170+/-10 nmol x g dry wt(-1) x min(-1) [corrected]. The Michaelis-Menten constant for binding of Na+ to the taurine transporter is concomitantly increased from 96+/-11 to 129+/-8 mM and the Na+:taurine coupling ratio for activation of the transport cycle is reduced from 3.3+/-0.6 to 2.4+/-0.2. This suggests that cal A-sensitive phosphatases maintain a high affinity of the taurine transporter towards Na+ and taurine as well as a high taurine transport capacity in unpertubated Ehrlich cells.

Animals↗
PubMed1997

Cell swelling activates phospholipase A2 in Ehrlich ascites tumor cells.

Ehrlich ascites tumor cells, loaded with 3H-labeled arachidonic acid and 14C-labeled stearic acid for two hours, were washed and transferred to either isotonic or hypotonic media containing BSA to scavenge the labeled fatty acids released from the cells. During the first two minutes of hypo-osmotic exposure the rate of 3H-labeled arachidonic acid release is 3.3 times higher than that observed at normal osmolality. Cell swelling also causes an increase in the production of 14C-stearic acid-labeled lysophosphatidylcholine. This indicates that a phospholipase A2 is activated by cell swelling in the Ehrlich cells. Within the same time frame there is no swelling-induced increase in 14C-labeled stearic acid release nor in the synthesis of phosphatidyl 14C-butanol in the presence of 14C-butanol. Furthermore, U7312, an inhibitor of phospholipase C, does not affect the swelling induced release of 14C-labeled arachidonic acid. Taken together these results exclude involvement of phospholipase A1, C and D in the swelling-induced liberation of arachidonic acid. The swelling-induced release of 3H-labeled arachidonic acid from Ehrlich cells as well as the volume regulatory response are inhibited after preincubation with GDP beta S or with AACOCF3, an inhibitor of the 85 kDa, cytosolic phospholipase A2. Based on these results we propose that cell swelling activates a phospholipase A2--perhaps the cytosolic 85 kDa type--by a partly G-protein coupled process, and that this activation is essential for the subsequent volume regulatory response.

Arachidonic Acid↗
PubMed1997

On the role of calcium in the regulatory volume decrease (RVD) response in Ehrlich mouse ascites tumor cells.

The putative role for Ca2+ entry and Ca2+ mobilization in the activation of the regulatory volume decrease (RVD) response has been assessed in Ehrlich cells. Following hypotonic exposure (50% osmolarity) there is: (i) no increase in cellular Ins(1,4,5)P3 content, as measured in extracts from [2-3H]myoinositol-labeled cells, a finding at variance with earlier reports from our group; (ii) no evidence of Ca2+-signaling recorded in a suspension of fura-2-loaded cells; (iii) Ca2+-signaling in only about 6% of the single, fura-2-loaded cells at 1-mm Ca2+ (1% only at 0.1-mM Ca2+ and in Ca2+-free medium), as monitored by fluorescence-ratio imaging; (iv) no effect of removing external Ca2+ upon the volume-induced K+ loss; (v) no significant inhibition of the RVD response in cells loaded with the Ca2+ chelator BAPTA when the BAPTA-loading is performed in K+ equilibrium medium; (vi) an inhibition of the swelling-induced K+ loss (about 50%) at 1-mM Ba2+, but almost no effect of charybdotoxin (100 nm) or of clotrimazole (10 microM), reported inhibitors of the K+ loss induced by Ca2+-mobilizing agonists. Thus, Ca2+signaling by Ca2+ release or Ca2+ entry appears to play no role in the activation mechanism for the RVD response in Ehrlich cells.

Animals↗
PubMed1997

Leukotriene D4-induced Ca2+ mobilization in Ehrlich ascites tumor cells.

Stimulation of Ehrlich ascites tumor cells with leukotriene D4 (LTD4) within the concentration range 1-100 nm leads to a concentration-dependent, transient increase in the intracellular, free Ca2+ concentration, [Ca2+]i. The Ca2+ peak time, i.e., the time between addition of LTD4 and the highest measured [Ca2+]i value, is in the range 0.20 to 0.21 min in ten out of fourteen independent experiments. After addition of a saturating concentration of LTD4 (100 nm), the highest measured increase in [Ca2+]i in Ehrlich cells suspended in Ca2+-containing medium is 260 +/- 14 nm and the EC50 value for LTD4-induced Ca2+ mobilization is estimated at 10 nM. Neither the peptido-leukotrienes LTC4 and LTE4 nor LTB4 are able to mimic or block the LTD4-induced Ca2+ mobilization, hence the receptor is specific for LTD4. Removal of Ca2+ from the experimental buffer significantly reduces the size of the LTD4-induced increase in [Ca2+]i. Furthermore, depletion of the intracellular Ins(1,4,5)P3-sensitive Ca2+ stores by addition of the ER-Ca2+-ATPase inhibitor thapsigargin also reduces the size of the LTD4-induced increase in [Ca2+]i in Ehrlich cells suspended in Ca2+-containing medium, and completely abolishes the LTD4-induced increase in [Ca2+]i in Ehrlich cells suspended in Ca2+-free medium containing EGTA. Thus, the LTD4-induced increase in [Ca2+]i in Ehrlich cells involves an influx of Ca2+ from the extracellular compartment as well as a release of Ca2+ from intracellular Ins(1,4,5)P3-sensitive stores. The Ca2+ peak times for the LTD4-induced Ca2+ influx and for the LTD4-induced Ca2+ release are recorded in the time range 0.20 to 0.21 min in four out of five experiments and in the time range 0.34 to 0.35 min in six out of eight experiments, respectively. Stimulation with LTD4 also induces a transient increase in Ins(1,4, 5)P3 generation in the Ehrlich cells, and the Ins(1,4,5)P3 peak time is recorded in the time range 0.27 to 0.30 min. Thus, the Ins(1,4, 5)P3 content seems to increase before the LTD4-induced Ca2+ release from the intracellular stores but after the LTD4-induced Ca2+ influx. Inhibition of phospholipase C by preincubation with U73122 abolishes the LTD4-induced increase in Ins(1,4,5)P3 as well as the LTD4-induced increase in [Ca2+]i, indicating that a U73122-sensitivity phospholipase C is involved in the LTD4-induced Ca2+ mobilization in Ehrlich cells. The LTD4-induced Ca2+ influx is insensitive to verapamil, gadolinium and SK&F 96365, suggesting that the LTD4-activated Ca2+ channel in Ehrlich cells is neither voltage gated nor stretch activated and most probably not receptor operated. In conclusion, LTD4 acts in the Ehrlich cells via a specific receptor for LTD4, which upon stimulation initiates an influx of Ca2+, through yet unidentified Ca2+ channels, and an activation of a U73122-sensitive phospholipase C, Ins(1,4,5)P3 formation and finally release of Ca2+ from the intracellular Ins(1,4,5)P3-sensitive stores.

Animals↗
PubMed1996

Phosphorylation is involved in the regulation of the taurine influx via the beta-system in Ehrlich ascites tumor cells.

The role of 3',5'-cyclic adenosine monophosphate (cAMP), protein kinase A (PKA), protein kinase C (PKC) and phosphatases in the regulation of the taurine influx via the beta-system in Ehrlich ascites tumor cells has been investigated. The taurine uptake by the beta-system in Ehrlich cells is inhibited when PKC is activated by phorbol 12-myristate 13-acetate (PMA) and when protein phosphatases are inhibited by calyculin A (CLA). On the other hand, taurine uptake by the beta-system is stimulated by an increased level of cAMP or following addition of N6,2'-O-dibutyryl-3',5'-cyclic adenosine monophosphate (dbcAMP). The effect of dbcAMP is partially blocked by addition of the protein kinase inhibitor H-89, and suppressed in the presence of CLA. It is proposed that the beta-system in the Ehrlich cells exists in three states of activity: State I, where a PKC phosphorylation site on the transporter or on a regulator is phosphorylated and transport activity is low. State II, where the PKC phosphorylation site is dephosphorylated and transport activity is normal. State III, representing a state with high transport activity, induced by an elevated cellular cAMP level. Apparently, cAMP preferentially stimulates taurine transport when the beta-system is in State II.

Animals↗
PubMed1996

Role of LTD4 in the regulatory volume decrease response in Ehrlich ascites tumor cells.

Stimulation with leukotriene D4 (LTD4) (3-100 nM) induces a transient increase in the free intracellular Ca2+ concentration ([Ca2+]i) in Ehrlich ascites tumor cells. The LTD4-induced increase in [Ca2+]i is, however, significantly reduced in Ca2+-free medium (2 mM EGTA), and under these conditions stimulation with a low LTD4 concentration (3 nM) does not result in any detectable increase in [Ca2+]i. Addition of LTD4 (3-100 nM) moreover accelerates the KCl loss seen during Regulatory Volume Decrease (RVD) in cells suspended in a hypotonic medium. The LTD4-induced (100 nM) acceleration of the RVD response is also seen in Ca2+-free medium and also at 3 nM LTD4, indicating that LTD4 can open K+- and Cl--channels without any detectable increase in [Ca2+]i. Buffering cellular Ca2+ with BAPTA almost completely blocks the LTD4-induced (100 nM) acceleration of the RVD response. Thus, the reduced [Ca2+]i level after BAPTA-loading or buffering of [Ca2+]i seems to inhibit the LTD4-induced stimulation of the RVD response even though the LTD4-induced cell shrinkage is not necessarily preceded by any detectable increase in [Ca2+]i. The LTD4 receptor antagonist L649, 923 (1 microM) completely blocks the LTD4-induced increase in [Ca2+]i and inhibits the RVD response as well as the LTD4-induced acceleration of the RVD response. When the LTD4 receptor is desensitized by preincubation with 100 nM LTD4, a subsequent RVD response is strongly inhibited. In conclusion, the present study supports the notion that LTD4 plays a role in the activation of the RVD response. LTD4 seems to activate K+ and Cl- channels via stimulation of a LTD4 receptor with no need for a detectable increase in [Ca2+]i.

Animals↗
PubMed1994

Cell swelling activates separate taurine and chloride channels in Ehrlich mouse ascites tumor cells.

The taurine efflux from Ehrlich ascites tumor cells is stimulated by hypotonic cell swelling. The swelling-activated taurine efflux is unaffected by substitution of gluconate for extracellular Cl- but inhibited by addition of MK196 (anion channel blocker) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; anion channel and anion exchange blocker) and by depolarization of the cell membrane. This is taken to indicate that taurine does not leave the osmotically swollen Ehrlich cells in exchange for extracellular Cl-, i.e., via the anion exchanger but via a MK196- and DIDS-sensitive channel that is potential dependent. An additional stimulation of the swelling-activated taurine efflux is seen after addition of arachidonic acid and oleic acid. Cell swelling also activates a "Mini Cl- channel." The Cl- efflux via this Cl- channel, in contrast to the swelling-activated taurine efflux, is unaffected by DIDS and inhibited by arachidonic acid and oleic acid. It is suggested that the swelling-activated "Mini Cl- channel" and the swelling-activated taurine channel in the Ehrlich cell represent two distinct types of channels.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

On the similarity between the small Cl- channel and the taurine channel activated after cell swelling in Ehrlich ascites tumor cells.

The swelling-activated Cl- efflux, mediated by the mini Cl- channel (3-7 pS), and the swelling-activated taurine efflux in Ehrlich cells are both inhibited by the anion channel blocker MK196 (indacrinone). The swelling-activated taurine efflux is also inhibited by DIDS and following depolarization of the cell membrane, but it is significantly stimulated by arachidonic acid in the micromolar range. The swelling-activated Cl- efflux is, in contrast, only slightly affected by DIDS, unaffected by the membrane potential, and completely blocked by arachidonic acid in the micromolar range. It is suggested that the swelling-activated mini Cl- channel and the taurine channel in the Ehrlich cells represent two distinct types of channels.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Volume regulation in human fibroblasts: role of Ca2+ and 5-lipoxygenase products in the activation of the Cl- efflux.

Trypsinized human skin fibroblasts in suspension perform regulatory volume decrease (RVD) after cell swelling in hypotonic medium. During RVD, 36Cl- efflux is dramatically increased and the cell membrane is depolarized, indicating the activation of Cl- channels. This activation of Cl- channels depends on extracellular as well as on intracellular Ca2+. The swelling-induced Cl- efflux and the RVD response are inhibited by the 5-lipoxygenase inhibitor ETH 615-139. Finally, following hypotonic treatment, cellular pH decreases. The pH decrease does not involve the Cl-/HCO3- exchange because it is independent of the external Cl- concentration.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

Relation between cytoskeleton, hypo-osmotic treatment and volume regulation in Ehrlich ascites tumor cells.

Pretreatment with cytochalasin B, which is known to disrupt microfilaments, significantly inhibits regulatory volume decrease (RVD) in Ehrlich ascites tumor cells, suggesting that an intact microfilament network is a prerequisite for a normal RVD response. Colchicine, which is known to disrupt microtubules, has no significant effect on RVD. Ehrlich cells have a cortical three-dimensional, orthogonal F-actin filament network which makes the cells look completely black in light microscopy following immunogold/silver staining using anti-actin antibodies. After addition of cytochalasin B, the stained cells get lighter with black dots localized to the plasma membrane and appearance of multiple knobby protrusions at cell periphery. Also, a significant decrease in the staining of the cells is seen after 15 min of RVD in hypotonic medium. This microfilament reorganization appears during RVD in the presence of external Ca2+ or Ca(2+)-ionophore A23187. It is, however, abolished in the absence of extracellular calcium, with or without prior depletion of intracellular Ca2+ stores. An effect of increased calcium influx might therefore be considered. The microfilament reorganization during RVD is abolished by the calmodulin antagonists pimozide and trifluoperazine, suggesting the involvement of calmodulin in the process. The microfilament reorganization is also prevented by addition of quinine. This quinine inhibition is overcome by addition of the K+ ionophore valinomycin.

Actin Cytoskeleton↗
PubMed1993

Regulation of taurine transport in Ehrlich ascites tumor cells.

Taurine influx is inhibited and taurine efflux accelerated when the cell membrane of Ehrlich ascites tumor cells is depolarized. Taurine influx is inhibited at acid pH partly due to the concomitant depolarization of the cell membrane partly due to a reduced availability of negatively charged free carrier. These results are in agreement with a 2Na,1C1,1taurine cotransport system which is sensitive to the membrane potential due to a negatively charged empty carrier. Taurine efflux from Ehrlich cells is stimulated by addition of LTD4 and by swelling in hypotonic medium. Cell swelling in hypotonic medium is known to result in stimulation of the leukotriene synthesis and depolarization of the cell membrane. The taurine efflux, activated by cell swelling, is dramatically reduced when the phospholipase A2 is inhibited indirectly by addition of the anti-calmodulin drug pimozide, or directly by addition of RO 31-4639. The inhibition is in both cases lifted by addition of LTD4. The swelling-induced taurine efflux is also inhibited by addition of the 5-lipoxygenase inhibitors ETH 615-139 and NDGA. It is concluded that the swelling-induced activation of the taurine leak pathway involves a release of arachidonic acid from the membrane phospholipids and an increased oxidation of arachidonic acid into leukotrienes via the 5-lipoxygenase pathway. LTD4 seems to act as a second messenger for the swelling induced activation of the taurine leak pathway either directly or indirectly via its activation of the Cl- channels, i.e., via a depolarization of the cell membrane.

Animals↗