Robust Electrophysiological Assays using Solid Supported Membranes: the Organic Cation Transporter OCT2

2011 ◽  
Vol 64 (1) ◽  
pp. 31 ◽  
Author(s):  
Olga Gaiko ◽  
Ingo Janausch ◽  
Sven Geibel ◽  
Henning Vollert ◽  
Petra Arndt ◽  
...  
Keyword(s):  
Cell Lines ◽  
Organic Cation ◽  
Chinese Hamster ◽  
Organic Cation Transporter ◽  
Supported Membranes ◽  
Cho Cell ◽  
Drug Candidates ◽  
Substrate Affinities ◽  
Solid Supported Membranes

An electrophysiological assay platform based on solid supported membranes (SSM) for the organic cation transporter (OCT) is presented. Stable Chinese hamster ovary (CHO) cell lines overexpressing the human (hOCT2) and rat transporters (rOCT2) were generated and validated. Membrane preparations from the cell lines were investigated using SSM-based electrophysiology. Baculovirus transfected insect cells (HighFive and Mimic Sf9) were also tested with the same assay but yielded less than optimal results. The assays were validated by the determination of substrate affinities and inhibition by standard inhibitors. The study demonstrates the suitability of the SSM-based electrophysiological OCT assay for rapid and automatic screening of drug candidates.

scholarly journals Recombinant γY278H Fibrinogen Showed Normal Secretion from CHO Cells, but a Corresponding Heterozygous Patient Showed Hypofibrinogenemia

2021 ◽  
Vol 22 (10) ◽  
pp. 5218
Author(s):  
Tomu Kamijo ◽  
Takahiro Kaido ◽  
Masahiro Yoda ◽  
Shinpei Arai ◽  
Kazuyoshi Yamauchi ◽  
...  
Keyword(s):  
Cell Lines ◽  
Cho Cells ◽  
Fibrinogen Level ◽  
Culture Media ◽  
Chinese Hamster ◽  
Plasma Fibrinogen ◽  
Enzyme Linked Immunosorbent Assay ◽  
Cho Cell ◽  
Accelerated Degradation ◽  
Heterozygous Patient

We identified a novel heterozygous hypofibrinogenemia, γY278H (Hiroshima). To demonstrate the cause of reduced plasma fibrinogen levels (functional level: 1.12 g/L and antigenic level: 1.16 g/L), we established γY278H fibrinogen-producing Chinese hamster ovary (CHO) cells. An enzyme-linked immunosorbent assay demonstrated that synthesis of γY278H fibrinogen inside CHO cells and secretion into the culture media were not reduced. Then, we established an additional five variant fibrinogen-producing CHO cell lines (γL276P, γT277P, γT277R, γA279D, and γY280C) and conducted further investigations. We have already established 33 γ-module variant fibrinogen-producing CHO cell lines, including 6 cell lines in this study, but only the γY278H and γT277R cell lines showed disagreement, namely, recombinant fibrinogen production was not reduced but the patients’ plasma fibrinogen level was reduced. Finally, we performed fibrinogen degradation assays and demonstrated that the γY278H and γT277R fibrinogens were easily cleaved by plasmin whereas their polymerization in the presence of Ca2+ and “D:D” interaction was normal. In conclusion, our investigation suggested that patient γY278H showed hypofibrinogenemia because γY278H fibrinogen was secreted normally from the patient’s hepatocytes but then underwent accelerated degradation by plasmin in the circulation.

Role of MAPK and PKA in regulation of rbOCT2-mediated renal organic cation transport

2007 ◽  
Vol 293 (1) ◽  
pp. F21-F27 ◽  
Author(s):  
Sunhapas Soodvilai ◽  
Atip Chatsudthipong ◽  
Varanuj Chatsudthipong
Keyword(s):  
Organic Cation ◽  
Chinese Hamster ◽  
Organic Cation Transporter ◽  
Inhibitory Effect ◽  
Cell System ◽  
Proximal Tubules ◽  
Common Pathway ◽  
Renal Proximal Tubules ◽  
Organic Cation Transporter 2 ◽  
Heterologous Cell

The effects of protein kinases MAPK and PKA on the regulation of organic cation transporter 2 (OCT2) were investigated both in a heterologous cell system [Chinese hamster ovary (CHO-K1) cells stably transfected with rabbit (rb)OCT2] and in native intact rabbit renal proximal S2 segments. Inhibition of MEK (by U-0126) or PKA (by H-89) reduced transport activity of rbOCT2 in CHO-K1 cells. The inhibitory effect of U-0126 combined with H-89 produced no additive effect, indicating that the action of PKA and MAPK in the regulation of rbOCT2 is in a common pathway. Activation of PKA by forskolin stimulated rbOCT2 activity, and this stimulatory effect was eliminated by H-89, indicating that the stimulation required PKA activation. In S2 segments of rabbit renal proximal tubules, activation of MAPK (by EGF) and PKA (by forskolin) stimulated activity of rbOCT2, and this activation was abolished by U-0126 and H-89, respectively. This is the first study to show that MAPK and PKA are involved, apparently in a common pathway, in the regulation of OCT2 activity in both a heterologous cell system and intact renal proximal tubules.

scholarly journals Pore mutants of HERG and KvLQT1 downregulate the reciprocal currents in stable cell lines

2010 ◽  
Vol 299 (5) ◽  
pp. H1525-H1534 ◽  
Author(s):  
Xiao-Qin Ren ◽  
Gong Xin Liu ◽  
Louise E. Organ-Darling ◽  
Renjian Zheng ◽  
Karim Roder ◽  
...  
Keyword(s):  
Cell Lines ◽  
Rabbit Model ◽  
Chinese Hamster ◽  
Expression Vectors ◽  
Delayed Rectifier ◽  
Wild Type ◽  
Cho Cell ◽  
Surface Plasmon Resonance Analysis ◽  
Transgenic Rabbit

We previously reported a transgenic rabbit model of long QT syndrome based on overexpression of pore mutants of repolarizing K+ channels KvLQT1 (LQT1) and HERG (LQT2).The transgenes in these rabbits eliminated the slow and fast components of the delayed rectifier K+ current ( IKs and IKr, respectively), as expected. Interestingly, the expressed pore mutants of HERG and KvLQT1 downregulated the remaining reciprocal repolarizing currents, IKs and IKr, without affecting the steady-state levels of the native polypeptides. Here, we sought to further explore the functional interactions between HERG and KvLQT1 in heterologous expression systems. Stable Chinese hamster ovary (CHO) cell lines expressing KvLQT1-minK or HERG were transiently transfected with expression vectors coding for mutant or wild-type HERG or KvLQT1. Transiently expressed pore mutant or wild-type KvLQT1 downregulated IKr in HERG stable CHO cell lines by 70% and 44%, respectively. Immunostaining revealed a severalfold lower surface expression of HERG, which could account for the reduction in IKr upon KvLQT1 expression. Deletion of the KvLQT1 NH2-terminus did not abolish the downregulation, suggesting that the interactions between the two channels are mediated through their COOH-termini. Similarly, transiently expressed HERG reduced IKs in KvLQT1-minK stable cells. Coimmunoprecipitations indicated a direct interaction between HERG and KvLQT1, and surface plasmon resonance analysis demonstrated a specific, physical association between the COOH-termini of KvLQT1 and HERG. Here, we present an in vitro model system consistent with the in vivo reciprocal downregulation of repolarizing currents seen in transgenic rabbit models, illustrating the importance of the transfection method when studying heterologous ion channel expression and trafficking. Moreover, our data suggest that interactions between KvLQT1 and HERG are mediated through COOH-termini.

scholarly journals Comparison of the mRNA sequences for Pi class glutathione transferases in different hamster species and the corresponding enzyme activities with anti-benzo[a]pyrene-7,8-dihydrodiol 9,10-epoxide

1996 ◽  
Vol 318 (2) ◽  
pp. 533-538 ◽  
Author(s):  
Stellan SWEDMARK ◽  
Bengt JERNSTRÖM ◽  
Dag JENSSEN
Keyword(s):  
Cell Lines ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Amino Acid Sequences ◽  
Cho Cell ◽  
Glutathione S Transferase ◽  
V79 Cells ◽  
Ovary Cells ◽  
Cdna Sequences ◽  
Chinese Hamster V79 Cells

Glutathione S-transferase (GST) of class Pi (GST Pi) is known to detoxify the mutagenic and carcinogenic (+)-anti-benzo[a]pyrene-7,8-dihydrodiol 9,10-epoxide [(+)-anti-BPDE] by conjugation with glutathione. Previously, we have shown that Chinese hamster V79 cells contain GST Pi, but seem to lack the capacity to conjugate (+)-anti-BPDE, although these cells do conjugate other substrates with GSH [Romert, Dock, Jenssen and Jernström (1989) Carcinogenesis 10, 1701–1707; Swedmark, Romert, Morgenstern and Jenssen (1992) Carcinogenesis 13, 1719–1723; Swedmark and Jenssen (1994) Gene 139, 251–256]. In the present study we have compared four cell lines derived from different hamster species with respect to GST cDNA sequences and capacity to conjugate (+)- or (-)-anti-BPDE. The cell lines were V79 and Chinese hamster ovary cells (CHO), Armenian hamster lung (AHL) cells and baby hamster kidney (BHK) cells. The sequencing revealed a complete homology between the V79 and CHO cDNA for GST Pi, whereas the corresponding amino acid sequences predicted from the corresponding AHL and BHK cDNAs differed by six and nine amino acids, respectively, from the predicted V79 sequence. None of these changes alone was found to influence the xenobiotic substrate-binding site. The cytosolic fractions from BHK and AHL cells were found to catalyse conjugation of (+)-anti-BPDE with GSH, whereas the corresponding activity in CHO cells was non-detectable. As shown previously, V79 cells were devoid of activity towards (+)-anti-BPDE. All the cell lines studied demonstrated appreciable GST activity towards 1-chloro-2,4-dinitrobenzene, but no activity with (-)-anti-BPDE. The latter result suggests that GST Pi is the sole or predominant GST in these cell lines. This was confirmed by HPLC analysis of purified enzymes obtained by affinity chromatography. However, when the catalytic activities of the pure enzymes were determined, all four different GST Pi enzymes were found to be highly capable of conjugating (+)-anti-BPDE with GSH. This observation indicates the existence of an intracellular factor that selectively inhibits conjugation of (+)-anti-BPDE, but not of 1-chloro-2,4-dinitrobenzene in the V79 and CHO cell lines. This new phenomenon seems to be specific for Chinese hamster, since both these cell lines originate from this species.

scholarly journals Evidence for intracellular partitioning of serine and glycine metabolism in Chinese hamster ovary cells

1996 ◽  
Vol 313 (3) ◽  
pp. 991-996 ◽  
Author(s):  
Michael R. NARKEWICZ ◽  
S. David SAULS ◽  
Susan S. TJOA ◽  
Cecilia TENG ◽  
Paul V. FENNESSEY
Keyword(s):  
Cell Lines ◽  
Chinese Hamster Ovary ◽  
Cho Cells ◽  
Chinese Hamster Ovary Cells ◽  
Mitochondrial Protein ◽  
Chinese Hamster ◽  
Serine Hydroxymethyltransferase ◽  
Cho Cell ◽  
Ovary Cells ◽  
Glycine Metabolism

Serine hydroxymethyltransferase (SHMT) is the primary enzyme in the interconversion of serine and glycine. The roles of mitochondrial and cytosolic SHMT in the interconversion of serine and glycine were determined in two Chinese hamster ovary (CHO) cell lines that both contain cytosolic SHMT but either have (CHOm+) or lack (CHOm-) mitochondrial SHMT. Mitochondrial SHMT activity was significantly reduced in CHOm- (0.24±0.11 nmol/min per mg of mitochondrial protein) compared with CHOm+ (3.21±0.66 nmol/min per mg of mitochondrial protein; P = 0.02) cells, whereas cytosolic SHMT activity was similar in CHOm- and CHOm+ cells (1.09±0.31 and 1.53±0.12 nmol/min per mg of cytosolic protein respectively; P = 0.57). In CHOm+ and CHOm- cells, the relative flux of glycine to serine measured with either [1-13C]- or [2-13C]-glycine was similar (CHOm-: 538±82 nmol/24 per mg of DNA; CHOm+: 616±88 nmol/24 h per mg of DNA; P = 0.42). In contrast, the relative flux of serine to glycine measured with [1-13C]serine was low in CHOm- cells (80±28 nmol/24 h per mg of DNA) compared with CHOm+ cells (3080±320 nmol/24 h per mg of DNA; P = 0.0001). The rate of glycine production determined by UA-2[1-13C]glycine dilution was lower in CHOm- (1200±200 nmol/24 h per mg of DNA) than CHOm+ (10200±1800 nmol/24 h per mg of DNA; P = 0.03) cells, whereas glycine utilization was similar in the two cell lines. Serine production was similar in the two cell lines but serine utilization was lower in CHOm- (3800±1200 μmol/24 h per mg of DNA) than CHOm+ (6600±1000 nmol/24 h per mg of DNA; P = 0.0002) cells. Increasing the serine concentration in the medium resulted in an increase in glycine production in CHOm+ but not in CHOm- cells. Intracellular studies with [1-13C]serine confirm the findings of decreased glycine production from serine. In CHO cells there is partitioning of intracellular serine and glycine metabolism. Our data support the hypothesis that mitochondrial SHMT is the primary pathway for serine into glycine interconversion.

scholarly journals Fluorescent organic cations for human OCT2 transporters screening: uptake in CHO cells stably expressing hOCT2

ADMET & DMPK ◽  
2017 ◽  
Vol 5 (2) ◽  
pp. 135 ◽  
Author(s):  
Malachy C. Ugwu ◽  
Ryan Pelis ◽  
Charles O. Esimone ◽  
Remigius U. Agu
Keyword(s):  
Cho Cells ◽  
Organic Cation ◽  
Rhodamine 6G ◽  
Chinese Hamster ◽  
Organic Cation Transporter ◽  
Rhodamine 123 ◽  
Intracellular Uptake ◽  
Wild Type ◽  
Transfected Cells ◽  
Organic Cation Transporter 2

<p class="ADMETabstracttext">The aim of this study was to assess the suitability of amiloride, rhodamine 6G and rhodamine 123 as non-radioactive substrates for characterizing hOCT2 using CHO cells. The uptake characteristics of these compounds were compared in wild-type (WT) and human organic cation transporter 2 (hOCT2)-stably transfected Chinese Hamster Ovary (CHO) cells. All the compounds were accumulated by the CHO-hOCT2 cells. Intracellular uptake of the compounds was higher in CHO cells stably-expressing hOCT2 compared to the WT. The uptake was concentration–dependent and saturable (except for rhodamine 123). The affinities of the compounds for the hOCT2 (in descending order) were: amiloride (K<sub>m</sub> = 72.63 ± 12.02 µM) &gt; rhodamine 6 G (K<sub>m</sub> = 82.47 ± 29.15 µM). Uptake of amiloride in transfected cells was pH -dependent and significantly inhibited by hOCT2 inhibitors (quinine, verapamil and quinidine). Based on our kinetic data and other considerations, we recommend the use of amiloride for characterizing hOCT2 transporters.</p>

scholarly journals Multiple mechanisms of ligand interaction with the human organic cation transporter, OCT2

2013 ◽  
Vol 304 (1) ◽  
pp. F56-F67 ◽  
Author(s):  
Jaclyn N. Harper ◽  
Stephen H. Wright
Keyword(s):  
Organic Cation ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Organic Cation Transporter ◽  
Ligand Interaction ◽  
Ovary Cells ◽  
Tandem Mass Spectroscopy ◽  
Mechanistic Basis ◽  
Independent Assessment ◽  
Structural Classes

OCT2 is the entry step for organic cation (OC) secretion by renal proximal tubules. Although many drugs inhibit OCT2 activity, neither the mechanistic basis of their inhibition nor their transport status is generally known. Using representatives of several structural classes of OCT2-inhibitory ligands described recently (Kido Y, Matsson P, Giacomini KM. J Med Chem 54: 4548–4558, 2011), we determined the kinetic basis of their inhibition of 1-methyl-4-phenylpyridinium (MPP) transport into Chinese hamster ovary cells that stably expressed hOCT2. The “cluster II” inhibitors (which contain known OCT2 substrates) metformin and cimetidine interacted competitively with MPP. However, other cluster II compounds, including tetraethylammonium (TEA), diphenidol and phenyltoloxamine, were mixed-type inhibitors of MPP transport (i.e., decreasing Jmax and increasing Kt). A cluster III (neutral steroid) representative, adrenosterone, and a cluster I (large, flexible cation) representative, carvedilol, displayed noncompetitive inhibitory profiles. Competitive counterflow (CCF) was used to determine whether the inhibitory ligands served as substrates of hOCT2. Carvedilol (cluster I) and adrenosterone (cluster III) did not support CCF, consistent with the prediction that members of these structural classes are likely to be nontransported inhibitors of OCT2. The cluster II representatives MPP, metformin, cimetidine, and TEA all supported CCF, consistent with independent assessments of their OCT2-mediated transport. However, the other cluster II representatives, diphenidol and phenyltoloxamine, failed to support CCF, suggesting that neither compound is transported by OCT2. An independent assessment of diphenidol transport (using liquid chromatography with tandem mass spectroscopy) confirmed this observation. The results underscore the caution required for development of predictive models of ligand interaction with multidrug transporters.

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