Frank Thevenod

Publications (7)25.42 Total impact

• Article: Cd2+ Block and Permeation in CaV3.1 (α1G) T-type Calcium Channels. A Candidate Mechanism for Cd2+ Influx.

  Kyle V Lopin, Frank Thevenod, Jessica C Page, Stephen W Jones
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  ABSTRACT: Cd(2+) is an industrial pollutant that can cause cytotoxicity in multiple organs. We have examined the effects of Cd(2+)(o) on permeation and gating in Ca(v)3.1 (α1G) channels, stably transfected in HEK 293 cells, using whole-cell recording. Using instantaneous I-V currents (measured following strong depolarization) to isolate effects on permeation, Cd(2+) rapidly blocked currents with 2 mM Ca(2+) in a voltage-dependent manner. The block caused by Cd(2+) is relieved at more hyperpolarized potentials, suggesting that Cd(2+) can permeate through the selectivity filter of the channel into the cytosol. In the absence of other permeant ions (Ca(2+) and Na(+) replaced by N-methyl D-glucamine) Cd(2+) carried sizable inward currents through Ca(v)3.1 channels (210 ± 20 pA at -60 mV with 2 mM Cd2+). Ca(v)3.1 channels have a significant 'window current' at this voltage (P(open) ~ 1%) making them a candidate pathway for Cd(2+) entry into cells during Cd(2+) exposure. Incubation with radiolabeled (109)Cd(2+)(o) confirmed that Ca(v)3.1 channels can lead to the uptake of Cd(2+)(o) into cells.
  Molecular pharmacology 09/2012; · 4.53 Impact Factor
• Article: Fe2+ Block and Permeation in CaV3.1 (α1G) T-type Calcium Channels. A Candidate Mechanism for Non-Tranferrin-mediated Fe2+ Influx.

  Kyle V Lopin, I Patrick Gray, Carlos A Obejero-Paz, Frank Thevenod, Stephen W Jones
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  ABSTRACT: Iron is a biologically essential metal, but excess iron can cause damage to the cardiovascular and nevous systems. We have examined the effects of Fe(2+)(o) on permeation and gating in Ca(V)3.1 channels, stably transfected in HEK 293 cells, using whole-cell recording. Precautions were taken to maintain iron in the Fe(2+) state (e. g., extracellular ascorbate). Using instantaneous I-V relations (measured following strong depolarization) to isolate effects on permeation, Fe(2+)(o) rapidly blocked currents with 2 mM Ca(2+)(o) in a voltage-dependent manner, described by a Woodhull model with K(D) = 2.5 mM at 0 mV and an apparent electrical distance δ = 0.17. Fe(2+)(o) also shifted activation to more depolarized voltages (by ~10 mV at 1.8 mM Fe(2+)(o)), somewhat more strongly than Ca(2+)(o) or Mg(2+)(o), consistent with a Gouy-Chapman-Stern model with a surface charge density σ = 1 e-/98 Å(2) and K(Fe) = 4.5 M(-1) for Fe(2+)(o). In the absence of Ca(2+)(o) (and with Na(+)(o) replaced by tetraethylammonium), Fe(2+) carried detectable whole-cell inward currents at millimolar concentrations (73 ± 7 pA at -60 mV with 10 mM Fe(2+)(o)). From a 2-site 3-barrier Eyring model for permeation in Ca(V)3.1, we estimate a transport rate for Fe(2+) of ~20 ions per second per open channel at -60 mV and pH 7.2, in 1 μM Fe(2+)(o) (with 2 mM Ca(2+)(o)). Since Ca(V)3.1 exhibits a significant 'window current' in that voltage range (PO ~1%), Ca(V)3.1 channels are a likely pathway for Fe(2+) entry into cells, at clinically relevant concentrations of Fe(2+)(o).
  Molecular pharmacology 09/2012; · 4.53 Impact Factor
• Source

  Available from: Abdullah Sener

  Article: Expression of the electrogenic Na+–HCO3−-cotransporters NBCe1-A and NBCe1-B in rat pancreatic islet cells

  Muhammad S. Soyfoo, Nurdan Bulur, Myrna Virreira, Karim Louchami, Pascale Lybaert, Raphael Crutzen, Jason Perret, Christine Delporte, Eleni Roussa, Frank Thevenod, Len Best, Allen P. Yates, Willy J. Malaisse, Abdullah Sener, Renaud Beauwens
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  ABSTRACT: It was recently proposed that, in rat pancreatic islets, the production of bicarbonate accounts for the major fraction of the carbon dioxide generated by the oxidative catabolism of nutrient insulin secretagogues. In search of the mechanism(s) supporting the membrane transport of bicarbonate, the possible role of the electrogenic Na+–HCO3 −-cotransporters NBCe1-A and NBCe1-B in rat pancreatic islet cells was investigated. Expression of NBCe1-A and NBCe1-B in rat pancreatic islet cells was documented by RT-PCR, western blotting, and immunocytochemistry. The latter procedure suggested a preferential localization of NBCe1-B in insulin-producing cells. Tenidap (3–100μM), previously proposed as an inhibitor of NBCe1-A-mediated cotransport in proximal tubule kidney cells, caused a concentration-related inhibition of glucose-stimulated insulin secretion. It also inhibited 2-ketoisocaproate-induced insulin release and to a relatively lesser extent, the secretory response to l-leucine. Tenidap (50–100μM) also inhibited the metabolism of d-glucose in isolated islets, increased 22Na net uptake by dispersed islet cells, lowered intracellular pH and provoked hyperpolarization of plasma membrane in insulin-producing cells. This study thus reveals the expression of the electrogenic Na+–HCO3 −-cotransporters NBCe1-A and NBCe1-B in rat pancreatic islet cells, and is consistent with the participation of such transporters in the process of nutrient-stimulated insulin secretion. KeywordsIslet function-Ion transport-Islet beta cell-Alpha cell
  Endocrine 04/2012; 35(3):449-458. · 1.42 Impact Factor
• Article: Cyclosporin a, but not FK506, induces osmotic lysis of pancreas zymogen granules, intra-acinar enzyme release, and lysosome instability by activating K+ channel.

  Wing-Kee Lee, Matthias Braun, Christian Langelüddecke, Frank Thévenod
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  ABSTRACT: The immunosuppressant tacrolimus (FK506) has improved pancreas allograft survival compared with cyclosporin A (CsA), possibly because of reduced acute pancreatitis following ischemia-reperfusion injury. Ion permeabilities in zymogen granule (ZG) membranes, including a KCNQ1 K channel, promote hormone-stimulated enzyme secretion. We investigated whether a differential modulation of ZG and lysosomal ion permeabilities and enzyme secretion by CsA/FK506 contributes to pancreatitis. Rat ZGs and lysosomes were isolated by gradient centrifugation, ion permeabilities assayed by osmotic lysis, and single-channel currents recorded in a planar lipid bilayer. Amylase release was measured in permeabilized acini and lysosomal cathepsin B release detected by immunoblotting. CsA (1-10 μM), but not FK506, enhanced ZGs osmotic lysis by selectively increasing K permeability up to 5-fold. Zymogen granule membrane K channels showed ∼2-fold increased single-channel open probability with CsA only. Cyclosporin A selectively increased basal (∼2-fold), but not cholecystokinin-octapeptide (1 nM)-induced amylase secretion in K medium only. Cyclosporin A (5 μM), but not FK506, increased cathepsin B release from lysosomes. Cyclosporin A selectively opens the ZG K channel and induces cathepsin B release from lysosomes, which cause increased in situ lysis of ZGs and may aggravate or fuel acute allograft pancreatitis following hypoxia-reperfusion injury.
  Pancreas 12/2011; 41(4):596-604. · 2.39 Impact Factor
• Article: Anoctamins.

  Karl Kunzelmann, Yuemin Tian, Joana Raquel Martins, Diana Faria, Patthara Kongsuphol, Jiraporn Ousingsawat, Frank Thevenod, Eleni Roussa, Jason Rock, Rainer Schreiber
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  ABSTRACT: Endogenous Ca(2+)-activated Cl(-) channels (CaCC) demonstrate biophysical and pharmacological properties that are well represented in cells overexpressing anoctamin 1 (Ano 1, TMEM16A), a protein that has been identified recently as CaCC. Proteins of the anoctamin family (anoctamin 1-10, TMEM16A-K) are widely expressed. The number of reports demonstrating their physiological and clinical relevance is quickly rising. Anoctamins gain additional interest through their potential role in cell volume regulation and malignancy. Available data suggest that Ano 1 forms stable dimers and probably liaise with accessory proteins such as calmodulin or other anoctamins. In order to understand how anoctamins produce Ca(2+)-activated Cl(-) currents, it will be necessary to obtain better insight into their molecular structure, interactions with partner proteins, and mode of activation.
  Pflügers Archiv - European Journal of Physiology 05/2011; 462(2):195-208. · 4.46 Impact Factor
• Article: Cadmium-induced DNA damage triggers G(2)/M arrest via chk1/2 and cdc2 in p53-deficient kidney proximal tubule cells.

  Ulrich Bork, Wing-Kee Lee, Anna Kuchler, Thomas Dittmar, Frank Thévenod
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  ABSTRACT: Carcinogenesis is a multistep process that is frequently associated with p53 inactivation. The class 1 carcinogen cadmium (Cd(2+)) causes renal cancer and is known to inactivate p53. G(2)/mitosis (M) arrest contributes to stabilization of p53-deficient mutated cells, but its role and regulation in Cd(2+)-exposed p53-deficient renal cells are unknown. In p53-inactivated kidney proximal tubule (PT) cells, comet assay experiments showed that Cd(2+) (50-100 microM) induced DNA damage within 1-6 h. This was associated with peak formation of reactive oxygen species (ROS) at 1-3 h, measured with dihydrorhodamine 123, and G(2)/M cell cycle arrest at 6 h, which were abolished by the antioxidant alpha-tocopherol (100 microM). Cd(2+)-induced G(2)/M arrest was enhanced approximately twofold on release from cell synchronization (double thymidine block or nocodazole) and resulted in approximately twofold increase of apoptosis, indicating that G(2)/M arrest mirrors DNA damage and toxicity. The Chk1/2 kinase inhibitor UCN-01 (0.3 microM), which relieves G(2)/M transition block, abolished Cd(2+)-induced G(2) arrest and increased apoptosis. This was accompanied by prevention of Cd(2+)-induced cyclin-dependent kinase cdc2 phosphorylation at tyrosine 15, as shown by immunofluorescence microscopy and immunoblotting. The data indicate that in p53-inactivated PT cells Cd(2+)-induced ROS formation and DNA damage trigger signaling of checkpoint activating kinases ataxia telangiectasia-mutated kinase (ATM) and ataxia telangiectasia and Rad3-related kinase (ATR) to cause G(2)/M arrest. This may promote survival of premalignant PT cells and Cd(2+) carcinogenesis.
  AJP Renal Physiology 11/2009; 298(2):F255-65. · 4.42 Impact Factor
• Article: Organic cation transporters OCT1, 2, and 3 mediate high-affinity transport of the mutagenic vital dye ethidium in the kidney proximal tubule.

  Wing-Kee Lee, Markus Reichold, Bayram Edemir, Giuliano Ciarimboli, Richard Warth, Hermann Koepsell, Frank Thévenod
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  ABSTRACT: The positively charged fluorescent dyes ethidium (Et(+)) and propidium (Pr(2+)) are widely used as DNA and necrosis markers. Et(+) is cytotoxic and mutagenic. The polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3) mediate electrogenic facilitated diffusion of small (< or =500 Da) organic cations with broad specificities. In humans, OCT2 mediates basolateral uptake by kidney proximal tubules (PT), whereas in rodents OCT1/2 are involved. In mouse kidney, perfused Et(+) accumulated predominantly in the S2/S3 segments of the PT, but not Pr(2+). In cells stably overexpressing human OCTs (hOCTs), Et(+) uptake was observed with K(m) values of 0.8 +/- 0.2 microM (hOCT1), 1.7 +/- 0.5 microM (hOCT2), and 2.0 +/- 0.5 microM (hOCT3), whereas Pr(2+) was not transported. Accumulation of Et(+) was inhibited by OCT substrates quinine, 3-methyl-4-phenylpyridinium (MPP(+)), cimetidine, and tetraethylammonium (TEA(+)). For hOCT1 and hOCT2, the IC(50) values for MPP(+), TEA(+), and cimetidine were higher than for inhibition of previously tested transported substrates. For hOCT2, the inhibition of Et(+) uptake by MPP(+) and cimetidine was shown to be competitive. Et(+) also inhibited transport of 0.1 microM [(3)H]MPP(+) by all hOCT isoforms with IC(50) values between 0.4 and 1.3 microM, and the inhibition of hOCT1-mediated uptake of MPP(+) by Et(+) was competitive. In Oct1/2(-/-) mice, Et(+) uptake in the PT was almost abolished. The data demonstrate that Et(+) is taken up avidly by the PT, which is mediated by OCT1 and/or OCT2. Considering the high affinity of OCTs for Et(+) and their strong expression in various organs, strict safety guidelines for Et(+) handling should be reinforced.
  American journal of physiology. Renal physiology 05/2009; 296(6):F1504-13. · 3.68 Impact Factor