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- Aizman, O, et al.
(author)
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Anatomical and physiological evidence for D-1 and D-2 dopamine receptor colocalization in neostriatal neurons
- 2000
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In: Nature Neuroscience. - : Springer Science and Business Media LLC. - 1097-6256 .- 1546-1726. ; 3:3, s. 226-230
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Journal article (peer-reviewed)abstract
- Despite the importance of dopamine signaling, it remains unknown if the two major subclasses of dopamine receptors exist on the same or distinct populations of neurons. Here we used confocal microscopy to demonstrate that virtually all striatal neurons, both in vitro and in vivo, contained dopamine receptors of both classes. We also provide functional evidence for such colocalization: in essentially all neurons examined, fenoldopam, an agonist of the D-1 subclass of receptors, inhibited both the Na+/K+ pump and tetrodotoxin (TTX)-sensitive sodium channels, and quinpirole, an agonist of the Dr subclass of receptors, activated TTX-sensitive sodium channels. Thus D-1 and D-2 classes of ligands may functionally interact in virtually all dopamine-responsive neurons within the basal ganglia.
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- Aizman, O, et al.
(author)
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Na,K-ATPase as a signal transducer
- 2003
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In: Annals of the New York Academy of Sciences. - : Wiley. - 0077-8923 .- 1749-6632. ; 986, s. 489-496
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Journal article (peer-reviewed)
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- Aizman, O., et al.
(author)
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Ouabain, a steroid hormone that signals with slow calcium oscillations
- 2001
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 98:23, s. 13420-13424
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Journal article (peer-reviewed)abstract
- The plant-derived steroid, digoxin, a specific inhibitor of Na,K-ATPase, has been used for centuries in the treatment of heart disease. Recent studies demonstrate the presence of a digoxin analog, ouabain, in mammalian tissue, but its biological role has not been elucidated. Here, we show in renal epithelial cells that ouabain, in doses causing only partial Na,K-ATPase inhibition, acts as a biological inducer of regular, low-frequency intracellular calcium ([Ca2+](i)) oscillations that elicit activation of the transcription factor, NF-KB. Partial inhibition of Na,K-ATPase using low extracellular K+ and depolarization of cells did not have these effects. Incubation of cells in Ca2+-free media, inhibition of voltage-gated calcium channels, inositol triphosphate receptor antagonism, and redistribution of actin to a thick layer adjacent to the plasma membrane abolished [Ca2+](i) oscillations, indicating that they were caused by a concerted action of inositol triphosphate receptors and capacitative calcium entry via plasma membrane channels. Blockade of ouabain-induced [C-a2+](i) oscillations prevented activation of NF-kappaB. The results demonstrate a new mechanism for steroid signaling via plasma membrane receptors and underline a novel role for the steroid hormone, ouabain, as a physiological inducer of [Ca2+](i) oscillations involved in transcriptional regulation in mammalian cells.
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- Andersson, R. M., et al.
(author)
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Modulation of Na+,K+-ATPase activity is of importance for RVD
- 2004
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In: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 180:4, s. 329-334
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Journal article (peer-reviewed)abstract
- Aim: This study was performed to examine the role of Na+,K+-ATPase activity for the adaptive response to cell swelling induced by hypoosmoticity, i.e. the regulatory volume decrease (RVD). Methods: The studies were performed on COS-7 cells transfected with rat Na+,K+-ATPase. To study changes in cell volume, cells were loaded with the fluorescent dye calcein and the intensity of the dye, following exposure to a hypoosmotic medium, was recorded with confocal microscopy. Results: Ouabain-mediated inhibition of Na+,K+-ATPase resulted in a dose dependent decrease in the rate of RVD. Total Rb-86(+) uptake as well as ouabain dependent Rb-86(+) uptake, used as an index of Na+,K+-ATPase dependent K+ uptake, was significantly increased during the first 2 min following exposure to hypoosmoticity. Since protein kinase C (PKC) plays an important role in the modulation of RVD, a study was carried out on COS-7 cells expressing rat Na+,K+-ATPase, where Ser23 in the catalytic alpha1 subunit of rat Na+,K+-ATPase had been mutated to Ala (S23A), abolishing a known PKC phosphorylation site. Cells expressing S23A rat Na+,K+-ATPase exhibited a significantly lower rate of RVD and showed no increase in Rb-86(+) uptake during RVD. Conclusion: Taken together, these results suggest that a PKC-mediated transient increase in Na+,K+-ATPase activity plays an important role in RVD.
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- Belusa, R, et al.
(author)
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Changes in Na(+)-K(+)-ATPase activity influence cell attachment to fibronectin
- 2002
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In: American journal of physiology. Cell physiology. - : American Physiological Society. - 0363-6143 .- 1522-1563. ; 282:2, s. C302-C309
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Journal article (peer-reviewed)abstract
- Most vital cellular functions are dependent on a fine-tuned regulation of intracellular ion homeostasis. Here we have demonstrated, using COS cells that were untransfected or transfected with wild-type rat ouabain-resistant Na+-K+-ATPase, that partial inhibition of Na+-K+-ATPase has a dramatic influence on cell attachment to fibronectin. Ouabain dose-dependently decreased attachment in untransfected cells and in cells expressing wild-type Na+-K+-ATPase, but not in cells expressing ouabain-insensitive Na+-K+-ATPase, whereas inhibition of Na+-K+-ATPase by lowering extracellular K+concentration decreased attachment in all three cell types. Thirty percent inhibition of Na+-K+-ATPase significantly attenuated attachment. Na+-K+-ATPase inhibition caused a sustained increase in the intracellular Ca2+concentration that obscured Ca2+transients observed in untreated cells during attachment. Inhibitors of Ca2+transporters significantly decreased attachment, but inhibition of Na+/H+exchanger did not. Ouabain reduced focal adhesion kinase autophosphorylation but had no effect on cell surface integrin expression. These results suggest that the level of Na+-K+-ATPase activity strongly influences cell attachment, possibly by an effect on intracellular Ca2+.
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