Liang Tao

Publications of Liang Tao

• Monocyte-endothelial adhesion is modulated by Cx43-stimulated ATP release from monocytes.

  Authors: Dongdong Yuan, Qin Wang, Dengpan Wu, Meiling Yu, Suzhi Zhang, Li Li, Liang Tao, Andrew L Harris

  Biochemical and biophysical research communications. 03/2012;

  Adhesion of circulating monocytes to vascular endothelial cells is a crucial event in development of vascular inflammatory conditions, including atherosclerosis. We investigated the roles ofAdhesion of circulating monocytes to vascular endothelial cells is a crucial event in development of vascular inflammatory conditions, including atherosclerosis. We investigated the roles of connexin43 (Cx43) and ATP release on monocyte-endothelial adhesion. Cx43 function and expression were manipulated by connexin channel inhibitors, overexpression and siRNA. Connexin channel inhibitors rapidly decreased ATP release from U937 monocytes and increased adhesion to human umbilical vein endothelial cells (HUVEC). Monocyte ATP release correlated with Cx43 expression, not with Cx37 expression. Exogenous adenosine (ADO) or ATP decreased adhesion, and inhibition of ATP conversion to ADO increased adhesion. We infer that monocyte Cx43 channel activity causes ATP release, likely via Cx43-containing hemichannels, and that ATP decreases adhesion via conversion to ADO. Inhibition of HUVEC connexin channel activity did not affect ATP release or adhesion. In contrast, expression of Cx43 protein in U937 cells enhanced adhesion. Thus, Cx43 channel function and expression have opposite effects: Cx43 channel function in monocytes, but not in HUVEC, rapidly decreases adhesion via ATP release and conversion to ADO, whereas Cx43 expression itself enhances adhesion. These studies suggest that local regulation of monocyte Cx43 activity within the vasculature can dynamically modulate the monocyte-endothelial adhesion that is an initiating event in vascular inflammatory pathologies, with the baseline adhesion set by Cx43 expression levels. This balance of rapid and tonic influences may be crucial in development of vascular pathologies.

• Gap junctions propagate opposite effects in normal and tumor testicular cells in response to cisplatin.

  Authors: Xiaoting Hong, Qin Wang, Yan Yang, Suping Zheng, Xuhui Tong, Suzhi Zhang, Liang Tao, Andrew L Harris

  Cancer letters. 11/2011; 317(2):165-71.

  Gap junctions propagate toxic effects among tumor cells during chemotherapy, but could also enhance killing of normal cells by the same mechanism. We show that the effect of gap junctionalGap junctions propagate toxic effects among tumor cells during chemotherapy, but could also enhance killing of normal cells by the same mechanism. We show that the effect of gap junctional intercellular communication (GJIC) on cisplatin toxicity differs between normal and tumor testicular cells. Downregulation of GJIC by each of several different manipulations (no cell contact, pharmacological inhibition, siRNA suppression) decreased cisplatin cytoxicity in tumor cells but enhanced it in normal cells. Enhanced toxicity due to GJIC downregulation in normal cells correlated with increased DNA interstrand crosslinks. Thus, GJIC protects normal cells from cisplatin toxicity while enhancing it in tumor cells, suggesting that enhancement/maintenance of GJIC increases therapeutic efficacy while decreasing off-target toxicity.

• Mechanism for modulation of gating of connexin26-containing channels by taurine.

  Authors: Darren Locke, Fabien Kieken, Liang Tao, Paul L Sorgen, Andrew L Harris

  The Journal of general physiology. 08/2011; 138(3):321-39.

  The mechanisms of action of endogenous modulatory ligands of connexin channels are largely unknown. Previous work showed that protonated aminosulfonates (AS), notably taurine, directly and reversiblyThe mechanisms of action of endogenous modulatory ligands of connexin channels are largely unknown. Previous work showed that protonated aminosulfonates (AS), notably taurine, directly and reversibly inhibit homomeric and heteromeric channels that contain Cx26, a widely distributed connexin, but not homomeric Cx32 channels. The present study investigated the molecular mechanisms of connexin channel modulation by taurine, using hemichannels and junctional channels composed of Cx26 (homomeric) and Cx26/Cx32 (heteromeric). The addition of a 28-amino acid "tag" to the carboxyl-terminal domain (CT) of Cx26 (Cx26(T)) eliminated taurine sensitivity of homomeric and heteromeric hemichannels in cells and liposomes. Cleavage of all but four residues of the tag (Cx26(Tc)) resulted in taurine-induced pore narrowing in homomeric hemichannels, and restored taurine inhibition of heteromeric hemichannels (Cx26(Tc)/Cx32). Taurine actions on junctional channels were fully consistent with those on hemichannels. Taurine-induced inhibition of Cx26/Cx32(T) and nontagged Cx26 junctional channels was blocked by extracellular HEPES, a blocker of the taurine transporter, confirming that the taurine-sensitive site of Cx26 is cytoplasmic. Nuclear magnetic resonance of peptides corresponding to Cx26 cytoplasmic domains showed that taurine binds to the cytoplasmic loop (CL) and not the CT, and that the CT and CL directly interact. ELISA showed that taurine disrupts a pH-dependent interaction between the CT and the CT-proximal half of the CL. These studies reveal that AS disrupt a pH-driven cytoplasmic interdomain interaction in Cx26-containing channels, causing closure, and that the Cx26CT has a modulatory role in Cx26 function.

• Connexin 32 and its derived homotypic gap junctional intercellular communication inhibit the migration and invasion of transfected HeLa cells via enhancement of intercellular adhesion.

  Authors: Jie Yang, Bing Liu, Qin Wang, Dongdong Yuan, Xiaoting Hong, Yan Yang, Liang Tao

  Molecular medicine reports. 06/2011; 4(5):971-9.

  The effects of connexin (Cx) and its derived homotypic gap junctional intercellular communication (GJIC) between tumor cells on the invasion of metastatic cancers and the underlying mechanisms remainThe effects of connexin (Cx) and its derived homotypic gap junctional intercellular communication (GJIC) between tumor cells on the invasion of metastatic cancers and the underlying mechanisms remain unclear. In this study, we investigated the influence of Cx32 and the homotypic GJIC mediated by this Cx on the migration, invasion and intercellular adhesion of transfected HeLa cells. The expression of Cx32 significantly increased cell adhesion and inhibited migration and invasion. The inhibition of GJIC by oleamide, a widely used GJIC inhibitor, reduced the enhanced adhesion and partly reversed the decreased migration and invasion that had been induced by Cx32 expression. Blockage of the p38 and extracellular signal-regulated kinase 1 and 2 mitogen-activated protein kinase (ERK1/2 MAPKs) pathways using their specific inhibitors attenuated the effects of Cx32, but not those of GJIC, on cell adhesion, migration and invasion. These results indicate that the homotypic GJIC mediated by Cx32, as well as the Cx itself, inhibit cell migration and invasion, most likely through the elevation of intercellular adhesion. The suppressive effect of Cx32 on the migration and invasion of cancer cells, but not that of its derived homotypic GJIC, partly depends on the activation of the p38 and the ERK1/2 MAPKs pathways.

• Berberine potentizes apoptosis induced by X-rays irradiation probably through modulation of gap junctions.

  Authors: Bing Liu, Qin Wang, Dong-dong Yuan, Xiao-ting Hong, Liang Tao

  Chinese medical journal. 04/2011; 124(8):1221-8.

  Clinical combination of some traditional Chinese medical herbs, including berberine, with irradiation is demonstrated to improve efficacy of tumor radiotherapy, yet the mechanisms for such effectClinical combination of some traditional Chinese medical herbs, including berberine, with irradiation is demonstrated to improve efficacy of tumor radiotherapy, yet the mechanisms for such effect remain largely unknown. The present study investigated the effect of berberine on apoptosis induced by X-rays irradiation and the relation between this effect and gap junction intercellular communication (GJIC). The role of gap junctions in the modulation of X-rays irradiation-induced apoptosis was explored by manipulation of connexin (Cx) expression, and gap junction function, using oleamide, a GJIC inhibitor, and berberine. In transfected HeLa cells, Cx32 expression increased apoptosis induced by X-rays irradiation, while inhibition of gap junction by oleamide reduced the irradiation responses, indicating the dependence of X-rays irradiation-induced apoptosis on GJIC. Berberine, at the concentrations without cytotoxicity, enhanced apoptosis induced by irradiation only in the presence of functional gap junctions. These results suggest that berberine potentizes cell apoptosis induced by X-rays irradiation, probably through enhancement of gap junction activity.

• Propofol depresses the cytotoxicity of X-ray irradiation through inhibition of gap junctions.

  Authors: Yuping Zhao, Bing Liu, Qin Wang, Dongdong Yuan, Yan Yang, Xiaoting Hong, Xudong Wang, Liang Tao

  Anesthesia and analgesia. 03/2011; 112(5):1088-95.

  General anesthetics (e.g., propofol) influence the therapeutic activity of intraoperative radiotherapy but the mechanism of the effects is largely unknown. It has been reported that propofol inhibitsGeneral anesthetics (e.g., propofol) influence the therapeutic activity of intraoperative radiotherapy but the mechanism of the effects is largely unknown. It has been reported that propofol inhibits gap junction (GJ) function briefly, and a functional GJ enhances the efficacy of radiotherapy in some cancer cells. Yet the mechanisms underlying the inhibition of GJ function by propofol and the influence of propofol on therapeutic activity of intraoperative radiotherapy are unknown. The role of propofol at clinically relevant concentrations in the modulation of radiograph-induced cytotoxicity in HeLa cells transfected with connexin 32 (Cx32) plasmid was explored by manipulation of connexin expression, GJ presence, and function. GJ function, Cx32 protein level, and Cx32 mRNA expression were determined by "Parachute" dye-coupling assay, Western blotting, and reverse transcriptase-polymerase chain reaction, respectively. Propofol significantly reduced radiograph-induced cytotoxicity only in the presence of functional GJ. Four-hour propofol exposure inhibited GJ function mainly by diminution of Cx32 protein levels but without influence on Cx32 mRNA expression. These results suggest that propofol inhibits the function of the GJ through the reduction of Cx32 protein levels by a transcription-independent mechanism. They further indicate that propofol depresses the cytotoxicity of radiograph irradiation through inhibition of GJ activity.

• The effects of 2-aminoethoxydiphenyl borate and diphenylboronic anhydride on gap junctions composed of Connexin43 in TM₄ sertoli cells.

  Authors: Yan Yang, Ming-Hui Cao, Qin Wang, Dong-Dong Yuan, Li Li, Liang Tao

  Biological & pharmaceutical bulletin. 01/2011; 34(9):1390-7.

  2-Aminoethoxydiphenyl borate (2-APB) has recently been demonstrated to inhibit gap junction (GJ) channels, whereas the underlying mechanisms are still unknown. Using mouse TM₄ Sertoli cell which2-Aminoethoxydiphenyl borate (2-APB) has recently been demonstrated to inhibit gap junction (GJ) channels, whereas the underlying mechanisms are still unknown. Using mouse TM₄ Sertoli cell which expresses connexin43 (Cx43), we explored the effects of 2-APB and its analogues on dye-coupling through junctional channels formed by Cx43 and on expression of Cx43. Exposure of the cells to 2-APB (1-50 µM) and one of its analogues diphenylboronic anhydride (DPBA) (1-30 µM) for 4 h leads to a significant decrease in dye coupling of GJ in a concentration-dependent manner. The inhibitory effects of 2-APB and DPBA are reversible since decreased GJ coupling resumes after the two compounds are washed out. The disfunction of GJ induced by 2-APB and DPBA is associated with a decrease in total amount of Cx43 protein and number of GJs on the cell membrane. 2-APB and DPBA do not alter Cx43 phosphorylation state and the level of Cx43 mRNA expression. The loss of Cx43 protein is prevented by either lysosomal or proteasomal inhibitor, suggesting that the decrease in Cx43 results from a 2-APB or DPBA-enhanced degradation of Cx43. The present results indicate that 2-APB and DPBA inhibit GJ communication through decreasing Cx43 expression in TM₄ cells.

• Effects of carvedilol on delayed rectifier and transient inactivating potassium currents in rat hippocampal CA1 neurons.

  Authors: Jing-Jing Duan, Qin Wang, Chun-Yu Deng, Su-Juan Kuang, Ru-Zhu Chen, Liang Tao

  Clinical and experimental pharmacology & physiology. 10/2010; 37(10):996-1003.

  1. The aims of the present study were to investigate the mechanism(s) underlying the protective effect of carvedilol against neural damage. 2. The transient inactivating potassium current (I(A) ) and1. The aims of the present study were to investigate the mechanism(s) underlying the protective effect of carvedilol against neural damage. 2. The transient inactivating potassium current (I(A) ) and the delayed rectifier potassium current (I(K) ) in rat hippocampal CA1 pyramidal neurons were recorded using whole-cell patch-clamp techniques. 3. Carvedilol (0.1-3 μmol/L) significantly inhibited I(K) with an IC(50) of 1.3 μmol/L and the inhibition was voltage independent. Over the same concentration range, carvedilol had no effect on the amplitude of I(A). At 1 μmol/L, carvedilol did not significantly change the steady state activation curves of I(A) and I(K), but did negatively shift their steady state inactivation curves. Recovery from inactivation was slowed for both I(A) and I(K). The inhibitory effect of carvedilol on I(K) was not affected by the adrenoceptor agonists phenylephrine and prazosin or the adrenoceptor antagonist isoproterenol, but propranolol was able to shift the dose-response curve of carvedilol for I(K) to the right. 4. Because I(K) is the main pathway for loss of intracellular potassium from depolarized neurons, selective obstruction of I(K) by carvedilol could be useful for neuroprotection.

• Cisplatin and oxaliplatin inhibit gap junctional communication by direct action and by reduction of connexin expression, thereby counteracting cytotoxic efficacy.

  Authors: Qin Wang, Tianhui You, Dongdong Yuan, Xu Han, Xiaoting Hong, Bo He, Lingzhi Wang, Xuhui Tong, Liang Tao, Andrew L Harris

  The Journal of pharmacology and experimental therapeutics. 03/2010; 333(3):903-11.

  Cisplatin [cis-diamminedichloroplatinum(II)]/oxaliplatin [1,2-diamminocyclohexane(trans-1)oxolatoplatinum(II)] toxicity is enhanced by functional gap junctions between treated cells, implying thatCisplatin [cis-diamminedichloroplatinum(II)]/oxaliplatin [1,2-diamminocyclohexane(trans-1)oxolatoplatinum(II)] toxicity is enhanced by functional gap junctions between treated cells, implying that inhibition of gap junctions may decrease cytotoxic activity of these platinum-based agents. This study investigates the effect of gap junction modulation by cisplatin/oxaliplatin on cytotoxicity in a transformed cell line. The effects were explored using junctional channels expressed in transfected HeLa cells and purified hemichannels. Junctional channels showed a rapid, dose-dependent decrease in dye coupling with exposure to cisplatin/oxaliplatin. With longer exposure, both compounds also decreased connexin expression. Both compounds inhibit the activity of purified connexin hemichannels, over the same concentration range that they inhibit junctional dye permeability, demonstrating that inhibition occurs by direct interaction of the drugs with connexin protein. Cisplatin/oxaliplatin reduced the clonogenic survival of HeLa cells at low density and high density in a dose-dependent manner, but to a greater degree at high density, consistent with a positive effect of gap junctional intercellular communication (GJIC) on cytotoxicity. Reduction of GJIC by genetic or pharmacological means decreased cisplatin/oxaliplatin toxicity. At low cisplatin/oxaliplatin concentrations, where effects on connexin channels are minimal, the toxicity increased with increased cell density. However, higher concentrations strongly inhibited GJIC, and this counteracted the enhancing effect of greater cell density on toxicity. The present results indicate that inhibition of GJIC by cisplatin/oxaliplatin decreases their cytotoxicity. Direct inhibition of GJIC and reduction of connexin expression by cisplatin/oxaliplatin may thereby compromise the effectiveness of these compounds and be a factor in the development of resistance to this class of chemotherapeutic agents.

• Suppressive Effect of Diazepam on IFN-gamma Production by Human T Cells.

  Authors: Min Wei, Li Li, Rui Meng, Yanying Fan, Yun Liu, Liang Tao, Xianguo Liu, Changyou Wu

  International immunopharmacology. 11/2009;

  Many studies showed that benzodiazepines could modulate immune responses through interaction with peripheral benzodiazepine receptors (PBRs) in immune cells but most of the studies were focused onMany studies showed that benzodiazepines could modulate immune responses through interaction with peripheral benzodiazepine receptors (PBRs) in immune cells but most of the studies were focused on monocytes and macrophages. In the present study, we revealed that diazepama mixed-type benzodiazepine, inhibited IFN-gamma production by human peripheral blood mononuclear cells (PBMCs) induced by anti-CD3 in dose-dependent manner. Flow cytometry analysis demonstrated that diazepam could inhibit the frequency of IFN-gamma-producing CD4(+) and CD8(+) T cells. The inhibitory effect of diazepam on IFN-gamma production is similar to that of R(0)5-4864, a selective PBRs ligand. However, D8555, a selective ligand for PBRs in microglia in the central nervous system, is a much weak inhibitor compared with R(0)5-4864 or diazepam. The inhibitory effect of R(0)5-4864 could be antagonized by PK11195, which is recognized as selective PBRs antagonist, and suppressive effect of diazepam on T cells is partially antagonized by PK11195. Collectively, these results suggested that diazepam suppressed human T cell function through PBRs.

• Tramadol and Flurbiprofen Depress the Cytotoxicity of Cisplatin via Their Effects on Gap Junctions.

  Authors: Bo He, Xuhui Tong, Lingzhi Wang, Qin Wang, Hua Ye, Bing Liu, Xiaoting Hong, Liang Tao, Andrew L Harris

  Clinical cancer research : an official journal of the American Association for Cancer Research. 10/2009;

  PURPOSE: Cancer patients are often concurrently treated with analgesics and antineoplastic drugs, yet the influence of analgesic agents on therapeutic activity of antineoplastic drugs is largelyPURPOSE: Cancer patients are often concurrently treated with analgesics and antineoplastic drugs, yet the influence of analgesic agents on therapeutic activity of antineoplastic drugs is largely unexplored. This study investigates the effects of three commonly used analgesics, which produce analgesia by different mechanisms, on cytotoxicity induced by cisplatin, a widely used antitumor agent, and the relation between those effects and modulation of gap junction function by the analgesics. EXPERIMENTAL DESIGN: The role of gap junctions in the modulation of cisplatin toxicity is explored by manipulation of connexin expression, and gap junction presence and function, using clinically relevant concentrations of the analgesics and cisplatin. RESULTS: Short-term exposure of transformed cells to cisplatin reduced the clonogenic survival in low-density cultures (without gap junction formation) and in high density (with gap junction formation), but the toxic effect was greater at high density. In the absence of connexin expression or with block of connexin channels, cell density had no effect on cisplatin toxicity. Tramadol and flurbiprofen, but not morphine, significantly reduced cisplatin cytotoxicity, but this effect required functional gap junctions between the cells. Tramadol and flurbiprofen inhibited dye-coupling through gap junctions, but morphine did not. CONCLUSIONS: The results suggest that the density dependence of cisplatin toxicity is mediated by gap junctions. They further indicate that tramadol and flurbiprofen depress cisplatin cytotoxicity through inhibition of gap junction activity, and more generally, that agents that depress junctional communication can counteract the effects of antitumor agents. (Clin Cancer Res 2009;15(18):OF1-8).

• Combined treatment with minocycline and prednisone attenuates experimental autoimmune encephalomyelitis in C57 BL/6 mice.

  Authors: Xiaohong Chen, Xueqiang Hu, Yan Zou, Rongbiao Pi, Mei Liu, Tieqiao Wang, Xueping Zheng, Meng Liu, Mingdong Lin, Peiqing Liu, Liang Tao

  Journal of neuroimmunology. 05/2009;

• Cryptotanshinone, a compound from Salvia miltiorrhiza modulates amyloid precursor protein metabolism and attenuates beta-amyloid deposition through upregulating alpha-secretase in vivo and in vitro.

  Authors: Zhengrong Mei, Fangyan Zhang, Liang Tao, Wenhua Zheng, Yingnan Cao, Zhaohe Wang, Shu Tang, Kang Le, Shaorui Chen, Rongbiao Pi, Peiqing Liu

  Neuroscience letters. 02/2009;

  The amyloid precursor protein (APP) is cleaved enzymatically by non-amyloidogenic and amyloidogenic pathways. alpha-Secretase cleaves APP within beta-amyloid protein (Abeta) sequence, resulting inThe amyloid precursor protein (APP) is cleaved enzymatically by non-amyloidogenic and amyloidogenic pathways. alpha-Secretase cleaves APP within beta-amyloid protein (Abeta) sequence, resulting in the release of a secreted fragment of APP (sAPPalpha) and precluding Abeta generation. Cryptotanshinone (CTS), an active component of the medicinal herb Salvia miltiorrhiza, has been shown to improve learning and memory in several pharmacological models of Alzheimer's disease (AD). However, the effects of CTS on the Abeta plaque pathology and the APP processing in AD are unclear. Here we reported that CTS strongly attenuated amyloid plaque deposition in the brain of APP/PS1 transgenic mice. In addition, CTS significantly improved spatial learning and memory in APP/PS1 mice assessed by the Morris water maze testing. To define the exact molecular mechanisms involved in the beneficial effects of CTS, we investigated the effects of the CTS on APP processing in rat cortical neuronal cells overexpressing Swedish mutant human APP695. CTS was found to decrease Abeta generation in concentration-dependent (0-10muM) manner. Interestingly, the N-terminal APP cleavage product, sAPPalpha was markedly increased by CTS. Further study showed that alpha-secretase activity was increased by CTS. Taken together, our results suggested CTS improved the cognitive ability in AD transgenic mice and promoted APP metabolism toward the non-amyloidogenic products pathway in rat cortical neuronal cells. CTS shows a promising novel way for the therapy of AD.

• 2-aminoethoxydiphenyl borate directly inhibits channels composed of connexin26 and/or connexin32.

  Authors: Liang Tao, Andrew L Harris

  Molecular pharmacology. 03/2007; 71(2):570-9.

  2-aminoethoxydiphenyl borate (2-APB), a commonly used blocker of IP3-induced calcium ion release and of store-operated channels, inhibits gap junction conductance when applied to cultured cells. The2-aminoethoxydiphenyl borate (2-APB), a commonly used blocker of IP3-induced calcium ion release and of store-operated channels, inhibits gap junction conductance when applied to cultured cells. The character and pharmacology of this inhibition was explored using 1) hemichannels composed of connexin32 (Cx32) and/or connexin26 (Cx26) purified from native sources and from transfected HeLa cells in which the connexin had a cleavable C-terminal epitope tag and 2) the corresponding junctional channels. Using reconstituted hemichannels in a liposome-based transport-specific fractionation assay (TSF), 2-APB reversibly inhibited homomeric Cx32 and heteromeric Cx26/Cx32 channels from native tissue and their tagged forms from HeLa cells. The IC50-TSF value of the inhibition was approximately 47 microM at pH 6.5. 2-APB did not inhibit tagged homomeric Cx26 channels even after tag cleavage (leaving several amino acids at the carboxyl terminus). Protonated 2-APB is the inhibitory agent, but channel sensitivity to 2-APB also increases as pH is lowered. To help define the chemical requirements for inhibition, the effects of four structural analogs of 2-APB were determined. The inhibitory action of 2-APB was shown to be distinct from that of aminosulfonates. 2-APB and its analogs, except phenytoin, inhibited dye-coupling through junctional channels formed by all the tagged channel forms except Cx26, consistent with the TSF studies. However 2-APB significantly inhibited dye coupling between cells expressing untagged Cx26, suggesting that an unmodified C terminus is required for action on Cx26 channels. These results show that protonated 2-APB directly and reversibly inhibits connexin channels composed of Cx26 and/or Cx32 and suggest involvement of the carboxyl-terminal domain.

• Kainate-activated currents in the ventral tegmental area of neonatal rats are modulated by interleukin-2.

  Authors: Jiang Hong Ye, Steven S Zalcman, Liang Tao

  Brain research. 08/2005; 1049(2):227-33.

  Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia,Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia, Parkinson's disease, autism, cognitive disorders) that are linked with abnormalities in these systems. Since the kainate receptor plays an essential role in mesolimbic neuronal development and excitability, we examined the effects of physiologically relevant concentrations of IL-2 on kainate-activated current (I(KA)) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA) of 3- to 14-day-old rats. IL-2 (0.01-10 ng/ml) alone had no effect on membrane conductance. When co-applied with kainate, IL-2 significantly decreased I(KA). IL-2 (2 ng/ml) shifted the kainate concentration-response curve to the right in a parallel manner, significantly increasing the EC(50) without changing the maximal I(KA). IL-2 inhibition of I(KA) was voltage-dependent, being greater at negative potentials. IL-2 did not alter the reversal potential. These findings suggest that IL-2 potently modulates kainate receptors of developing mesolimbic neurons. We suggest that IL-2 plays a role in the excitability of developing neurons in the mesolimbic system. Inasmuch as increased I(KA) is associated with excitotoxicity, coupled with the present observation that IL-2 inhibits I(KA), we suggest an adaptive role for IL-2 in limiting excitotoxicity in the developing brain. IL-2 might thus be required for normal cell development in the mesolimbic and mesostriatal systems.

• Biochemical requirements for inhibition of Connexin26-containing channels by natural and synthetic taurine analogs.

  Authors: Liang Tao, Andrew L Harris

  The Journal of biological chemistry. 10/2004; 279(37):38544-54.

  Previous work has shown that protonated taurine and aminosulfonate pH buffers, including HEPES, can directly and reversibly inhibit connexin channels that contain connexin26 (Cx26) (Bevans, C. G.,Previous work has shown that protonated taurine and aminosulfonate pH buffers, including HEPES, can directly and reversibly inhibit connexin channels that contain connexin26 (Cx26) (Bevans, C. G., and Harris, A. L. (1999) J. Biol. Chem. 274, 3711-3719). The structural requirements for this inhibition were explored by studies of the effects of structural analogs of taurine on the activity of Cx26-containing reconstituted hemichannels from native tissue. Several analogs inhibited the channels, with a range of relative affinities and efficacies. Each active compound contains a protonated amine separated from an ionized sulfonate or sulfinate moiety by several methylene groups. The inhibition is eliminated if the sulfonate/sulfinate moiety or the amine is not present. Compounds that contain a protonated amine but lack a sulfonate/sulfinate moiety do not inhibit but do competitively block the effect of the active compounds. Compounds that lack the protonated amine do not significantly inhibit or antagonize inhibition. The results suggest involvement of the protonated amine in binding and of the ionized sulfur-containing moiety in effecting the inhibition. The maximal effect of the inhibitory compounds is enhanced when a carboxyl group is linked to the alpha-carbon. Inhibition but not binding is stereospecific, with l-isomers being inhibitory and the corresponding d-isomers being inactive but able to antagonize inhibition by the l-isomers. Whereas not all connexins are sensitive to aminosulfonates, the well defined structural requirements described here argue strongly for a highly specific regulatory interaction with some connexins. The finding that cytoplasmic aminosulfonates inhibit connexin channels whereas other cytoplasmic compounds antagonize the inhibition suggests that gap junction channels are regulated by a complex interplay of cytoplasmic ligands.

• Inhibition of glycine receptor function of native neurons by aliphatic n-alcohols.

  Authors: Liang Tao, Jiang Hong Ye

  British journal of pharmacology. 07/2002; 136(4):629-35.

  The inhibitory effects of n-alcohols (methanol to dodecanol) on glycine-activated currents were studied in neurons freshly dissociated from the ventral tegmental area of neonatal rats usingThe inhibitory effects of n-alcohols (methanol to dodecanol) on glycine-activated currents were studied in neurons freshly dissociated from the ventral tegmental area of neonatal rats using whole-cell patch-clamp recording technique. Ethanol enhanced and depressed glycine-activated currents in 35% and 45%, respectively, of neurons of ventral tegmental area of neonatal rats. In this report, we extended our focus of ethanol-induced inhibition of glycine currents to other straight-chain alcohols. Aliphatic n-alcohols, which have carbon numbers less than nine, suppressed glycine currents in 45% (71/158) of the neurons. All results from this study are obtained from the 45% of cells displaying inhibition; the other 55% of the neurons were not studied. Alcohol potency increased as the number of carbon atoms increased from one to five, and was at a maximal plateau from five to nine; alcohols with 10 or more carbons did not inhibit glycine-activated currents. Thus, a 'cutoff' point in their potency for inhibition of glycine receptor function occurred at about decanol. A coapplication of dodecanol with ethanol eliminated the inhibition resulting from ethanol. Thus, dodecanol may bind to the receptor silently and compete with ethanol. These observations indicate that straight-chain n-alcohols exhibit a 'cutoff' point in their potency for inhibition of the glycine receptor function between nine and 10 carbon atoms. The inability of longer alcohols to change the activation properties of the receptors may contribute to the cutoff effect.

• Protein kinase C modulation of ethanol inhibition of glycine-activated current in dissociated neurons of rat ventral tegmental area.

  Authors: Liang Tao, Jiang Hong Ye

  The Journal of pharmacology and experimental therapeutics. 04/2002; 300(3):967-75.

  The brain is particularly sensitive to alcohol during its growth spurt period. To better understand the mechanism(s) involved, we studied the effects of ethanol on neurons freshly dissociated fromThe brain is particularly sensitive to alcohol during its growth spurt period. To better understand the mechanism(s) involved, we studied the effects of ethanol on neurons freshly dissociated from the ventral tegmental area (VTA) in neonatal rats. Ethanol enhanced (35%) or depressed (45%) glycine-induced responses in VTA neurons (Ye et al., 2001a, 2001b). In this report, we investigated the role of protein kinase C (PKC) and protein kinase A (PKA) in ethanol-induced inhibition of glycine-activated current, using whole-cell patch-clamp technique. Ethanol inhibited glycine-activated current when it was coapplied with the agonist. This inhibition was enhanced when neurons were pretreated with ethanol before the subsequent coapplication of ethanol and glycine. Ethanol's inhibition of glycine-activated currents increased with the length of ethanol pretreatment time (ranging from 1 to 30 s), and reached the maximum at 30 s. However, this enhanced inhibition was not seen in the absence of internal ATP. In addition, phorbol-12-myristate-13-acetate (PMA, 100 nM), a PKC activator, markedly inhibited glycine-activated current. Blockade of PKC by chelerythrine or by PKC inhibitor peptide significantly attenuated ethanol-induced inhibition. Although partial increase of PKC activity by 1 nM PMA enhanced ethanol inhibition, pretreatment of ethanol did not increase ethanol inhibition after the neurons were treated with 100 nM PMA. These data suggest that ethanol and PKC share the same pathway to suppress glycine receptors. H-89 (1 microM), a selective PKA inhibitor, did not alter glycine-activated current or ethanol inhibition. Our observations suggest that activation of PKC (but not PKA) contributes to ethanol-induced inhibition of glycine receptors.

• Interleukin-2 modulates N-methyl-d-aspartate receptors of native mesolimbic neurons

  Authors: Jiang Hong Ye, Liang Tao, Steven S. Zalcman

  Brain Research.

  Interleukin (IL)-2 is a brain-derived cytokine that influences mesocorticolimbic dopamine release, and is associated with pathological outcomes that are mediated, at least in part, by aberrations inInterleukin (IL)-2 is a brain-derived cytokine that influences mesocorticolimbic dopamine release, and is associated with pathological outcomes that are mediated, at least in part, by aberrations in mesolimbic neurotransmission. The mechanisms by which IL-2 modulates mesolimbic transmission, however, are not known. The NMDA receptor/channel (NMDAR) plays an essential role in neuronal excitability of mesolimbic neurons; we thus examined in neonatal rats the effects of IL-2 on NMDA-activated current (INMDA) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA), the site of origin of the mesolimbic system. IL-2 (0.01–500 ng/ml) alone had no effect on membrane conductance. When co-applied with NMDA, IL-2 (50–500 ng/ml) significantly potentiated INMDA. In contrast, doses as low as 0.01 ng/ml markedly decreased the NMDA response. Dose–response analysis showed that IL-2 (>50 ng/ml) increased the maximal INMDA, without changing the EC50, indicating that IL-2 potentiates INMDA by increasing the efficacy of the NMDAR. Moreover, current–voltage analysis revealed that IL-2 potentiation of INMDA was voltage-dependent, being greater at negative potentials. In contrast, IL-2 inhibition of INMDA was voltage-independent, and IL-2 did not alter the reversal potential. Additionally, IL-2 (1 ng/ml) shifted the NMDA concentration–response curve to the right, significantly increasing the EC50 for NMDA without changing the maximal INMDA, suggesting that IL-2 inhibits the NMDAR by a competitive mechanism. IL-2 thus acts as a potent modulator of the NMDAR. IL-2-induced alterations of responses to NMDAR activation may contribute to synaptic plasticity in the mesolimbic system and to pathological outcomes associated with this system.

• Kainate-activated currents in the ventral tegmental area of neonatal rats are modulated by interleukin-2

  Authors: Jiang-Hong Ye, Steven S. Zalcman, Liang Tao

  Brain Research.

  Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia,Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia, Parkinson's disease, autism, cognitive disorders) that are linked with abnormalities in these systems. Since the kainate receptor plays an essential role in mesolimbic neuronal development and excitability, we examined the effects of physiologically relevant concentrations of IL-2 on kainate-activated current (IKA) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA) of 3- to 14-day-old rats. IL-2 (0.01–10 ng/ml) alone had no effect on membrane conductance. When co-applied with kainate, IL-2 significantly decreased IKA. IL-2 (2 ng/ml) shifted the kainate concentration–response curve to the right in a parallel manner, significantly increasing the EC50 without changing the maximal IKA. IL-2 inhibition of IKA was voltage-dependent, being greater at negative potentials. IL-2 did not alter the reversal potential. These findings suggest that IL-2 potently modulates kainate receptors of developing mesolimbic neurons. We suggest that IL-2 plays a role in the excitability of developing neurons in the mesolimbic system. Inasmuch as increased IKA is associated with excitotoxicity, coupled with the present observation that IL-2 inhibits IKA, we suggest an adaptive role for IL-2 in limiting excitotoxicity in the developing brain. IL-2 might thus be required for normal cell development in the mesolimbic and mesostriatal systems.