Differential contribution of sialic acid to the function of repolarizing K+ currents in ventricular myocytes

2001 ◽  
Vol 281 (2) ◽  
pp. C464-C474 ◽  
Author(s):  
Carmen A. Ufret-Vincenty ◽  
Deborah J. Baro ◽  
L. F. Santana
Keyword(s):  
Sialic Acid ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Chinese Hamster ◽  
Ovary Cell ◽  
Early Afterdepolarizations ◽  
Kv4 Channels ◽  
Ovary Cell Line ◽  
Differential Contribution ◽  
K Currents

We investigated the contribution of sialic acid residues to the K+ currents involved in the repolarization of mouse ventricular myocytes. Ventricular K+ currents had a rapidly inactivating component followed by slowly decaying and sustained components. This current was produced by the summation of three distinct currents: I to, which contributed to the transient component; I ss, which contributed to the sustained component; and I K,slow, which contributed to both components. Incubation of ventricular myocytes with the sialidase neuraminidase reduced the amplitude of I to without altering I K,slow and I ss. We found that the reduction in I to amplitude resulted from a depolarizing shift in the voltage of activation and a reduction in the conductance of I to. Expression of Kv4.3 channels, a major contributor to I to in the ventricle, in a sialylation-deficient Chinese hamster ovary cell line (lec2) mimicked the effects of neuraminidase on the ventricular I to. Furthermore, we showed that sialylated glycolipids have little effect on the voltage dependence of I to. Finally, consistent with its actions on I to, neuraminidase produced an increase in the duration of the action potential of ventricular myocytes and the frequency of early afterdepolarizations. We conclude that sialylation of the proteins forming Kv4 channels is important in determining the voltage dependence and conductance of I to and that incomplete glycosylation of these channels could lead to arrhythmias.

scholarly journals Assignment of the human dihydrofolate reductase gene to the q11----q22 region of chromosome 5.

1984 ◽  
Vol 4 (10) ◽  
pp. 2010-2016 ◽  
Author(s):  
V L Funanage ◽  
T T Myoda ◽  
P A Moses ◽  
H R Cowell
Keyword(s):  
Dihydrofolate Reductase ◽  
Hybrid Cell ◽  
Chinese Hamster ◽  
Ovary Cell ◽  
Chromosome 5 ◽  
Dhfr Gene ◽  
Reductase Gene ◽  
Ovary Cell Line ◽  
Biochemical Analyses ◽  
Human Dihydrofolate Reductase

Cells from a dihydrofolate reductase-deficient Chinese hamster ovary cell line were hybridized to human fetal skin fibroblast cells. Nineteen dihydrofolate reductase-positive hybrid clones were isolated and characterized. Cytogenetic and biochemical analyses of these clones have shown that the human dihydrofolate reductase (DHFR) gene is located on chromosome 5. Three of these hybrid cell lines contained different terminal deletions of chromosome 5. An analysis of the breakpoints of these deletions has demonstrated that the DHFR gene resides in the q11----q22 region.

Complementation of a methotrexate uptake defect in Chinese hamster ovary cells by DNA-mediated gene transfer

1989 ◽  
Vol 9 (4) ◽  
pp. 1754-1758
Author(s):  
T M Underhill ◽  
W F Flintoff
Keyword(s):  
Gene Transfer ◽  
Dna Sequences ◽  
Chinese Hamster Ovary ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Ovary Cell ◽  
Wild Type ◽  
Ovary Cells ◽  
Ovary Cell Line ◽  
Human Specific

A methotrexate-resistant Chinese hamster ovary cell line deficient in methotrexate uptake has been complemented to methotrexate sensitivity by transfection with DNA isolated from either wild-type Chinese hamster ovary or human G2 cells. Primary and secondary transfectants regained the ability to take up methotrexate in a manner similar to that of wild-type cells, and in the case of those transfected with human DNA, to contain human-specific DNA sequences. The complementation by DNA-mediated gene transfer of this methotrexate-resistant phenotype provides a basis for the cloning of a gene involved in methotrexate uptake.

scholarly journals Generating FSH antagonists and agonists through immunization against FSH receptor N-terminal decapeptides

1999 ◽  
Vol 22 (2) ◽  
pp. 151-159 ◽  
Author(s):  
L Abdennebi ◽  
L Couture ◽  
D Grebert ◽  
E Pajot ◽  
R Salesse ◽  
...  
Keyword(s):  
Chinese Hamster ◽  
Biochemical Properties ◽  
Ovary Cell ◽  
Fsh Receptor ◽  
Female Mice ◽  
Specific Receptors ◽  
Ovary Cell Line ◽  
G Protein Coupled ◽  
Follicle Maturation ◽  
Receptor Family

Follicle-stimulating hormone (FSH) via interaction with G-protein coupled specific receptors plays a central role in the control of gametogenesis in mammals of both sexes. In females, FSH is crucial for follicle growth, follicle maturation and ovulation. FSH receptors, together with luteinizing hormone-chorionic gonadotropin and thyrotropin receptors belong to a subfamily of structurally related receptors within the seven transmembrane receptor family. Among several other regions, the N-terminus of these receptors is believed to be responsible for important specific hormone-receptor contact sites. Recombinant filamentous phages displaying at their surface three overlapping N-terminal decapeptides of the FSH receptor, peptides A18-27, B25-34 and C29-38 were constructed. Ewes and female mice were immunized against the three FSH receptor (FSHR) recombinant phages. Immunoglobulins purified from immunized animals were analyzed for their biochemical properties on a Chinese hamster ovary cell line expressing the porcine FSH receptor. AntiA and antiB immunoglobulins (IgGs) behave as antagonists for 125I-FSH binding and for FSH-dependent cAMP production, while antiC IgGs did not compete for hormone binding. By contrast, antibodies against the C29-38 peptide displayed FSH agonist activity and stimulated the FSH receptor, whereas antiA and antiB IgGs did not. Furthermore, when the FSHR phages were used as peptidic vaccines, they induced a reversible inhibition of ovulation rate in ewes, and impaired fertility in female mice.

CCK receptor phosphorylation exposes regulatory domains affecting phosphorylation and receptor trafficking

2000 ◽  
Vol 279 (6) ◽  
pp. C1986-C1992 ◽  
Author(s):  
Rammohan V. Rao ◽  
Eileen L. Holicky ◽  
Susan M. Kuntz ◽  
Laurence J. Miller
Keyword(s):  
G Protein ◽  
Chinese Hamster ◽  
G Protein Coupled Receptors ◽  
Receptor Internalization ◽  
Ovary Cell ◽  
Guanine Nucleotide Binding Protein ◽  
Receptor Phosphorylation ◽  
Regulatory Domains ◽  
Ovary Cell Line ◽  
G Protein Coupled

Agonist-stimulated phosphorylation of guanine nucleotide-binding protein (G protein)-coupled receptors has been recognized as an important mechanism for desensitization by interfering with coupling of the activated receptor with its G protein. We recently described a mutant of the CCK receptor that modified two of five key sites of phosphorylation (S260,264A) and eliminated agonist-stimulated receptor phosphorylation, despite normal ligand binding and signaling (20). As expected, this nonphosphorylated mutant had impaired rapid desensitization but was ultimately able to be desensitized by normal receptor internalization. Here we demonstrate that this mutant receptor is also defective in resensitization, with abnormal recycling to the cell surface. To explore this, another receptor mutant was prepared, replacing the same serines with aspartates to mimic the charge of serine-phosphate (S260,264D). This mutant was expressed in a Chinese hamster ovary cell line and shown to bind CCK normally. It had accelerated kinetics of signaling and desensitization and was phosphorylated in response to agonist occupation, with all other normal sites of phosphorylation modified. It was internalized like wild-type receptors and was resensitized and trafficked normally. This provides evidence for an additional important function for phosphorylation of G protein-coupled receptors. Phosphorylation may induce a conformational change in the receptor to expose other potential sites of phosphorylation and to expose domains involved in the targeting and trafficking of endosomes. The hierarchical phosphorylation of these sites may play a key role in receptor regulation.

Multiple origins of replication in the dihydrofolate reductase amplicons of a methotrexate-resistant chinese hamster cell line

1990 ◽  
Vol 10 (4) ◽  
pp. 1338-1346
Author(s):  
C Ma ◽  
T H Leu ◽  
J L Hamlin
Keyword(s):  
Cell Line ◽  
Dihydrofolate Reductase ◽  
Chinese Hamster ◽  
Chinese Hamster Cell ◽  
Ovary Cell ◽  
Multiple Origins ◽  
Chromosomal Walking ◽  
Chinese Hamster Cell Line ◽  
S Period ◽  
Ovary Cell Line

We recently showed that replication initiates in the early S period at two closely spaced zones in the 240-kilobase (kb) dihydrofolate reductase (DHFR) amplicon of the methotrexate-resistant Chinese hamster ovary cell line CHOC 400. Both of these initiation loci (ori-beta and ori-gamma) have previously been cloned in a recombinant cosmid. In this study, we identified a third early-firing initiation locus (ori-alpha) in the much larger DHFR amplicon of the independently isolated methotrexate-resistant Chinese hamster cell line DC3F-A3/4K (A3/4K). We describe the molecular cloning of this newly identified locus and demonstrate by chromosomal walking that ori-alpha lies approximately 240 kb upstream from ori-beta. Using overlapping cosmid clones for more than 450 kb of DNA sequence from this region of the DHFR domain, we have monitored the replication pattern of the amplicons in synchronized A3/4K cells. These studies suggest that ori-alpha, ori-beta, and ori-gamma are the only early-firing initiation sites in this 450-kb sequence. In addition, we have been able to roughly localize the termini between ori-alpha and ori-beta and between ori-alpha and the next origin in the 5' direction. Thus, we have now isolated the equivalent of three early-firing replicons (including their origins) from a well-characterized chromosomal domain. With these tools, it should be possible to determine those properties that are shared by the origins and termini of different replicons and which are therefore likely to be functionally significant.

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