Abstract
Astrocytes have been shown to express endothelin (ET) receptors functionally coupled, via different heterotrimeric G proteins, to several intracellular pathways. To assess the relative contribution of each subtype in the astrocytic responses to ET-1, effects of BQ123, an antagonist selective for the ET receptor subtype A (ETA-R), and IRL1620, an agonist selective for the ET receptor subtype B (ETB-R), were investigated in primary cultures of rat astrocytes. Binding experiments indicated that the ETB-R is the predominant subtype in these cells. Inhibition of forskolin-stimulated cyclic AMP production was observed under. ETB-R stimulation. Bordetella pertussis toxin (PTX) pretreatment completely abolished this effect, indicating that this pathway is coupled to the ETB-R via Gi protein. Increases of tyrosine phosphorylation of cellular proteins, stimulation of mitogen-activated protein kinase (MAPK), and DNA synthesis were also found to be mediated by the ETB-R, but through PTX-insensitive G protein. IRL1620-induced MAPK activation involved the adapter proteins Shc and Grb2 and the serine/threonine kinase Raf-1. This study reveals that the various effects of ET-1 in astrocytes are mediated by the ETB-R, which couples to multiple signaling pathways including the MAPK cascade.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing*
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Animals
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Astrocytes / drug effects
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Astrocytes / metabolism*
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Calcium-Calmodulin-Dependent Protein Kinases / pharmacology*
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Cells, Cultured
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Cyclic AMP / antagonists & inhibitors
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DNA / biosynthesis*
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Electrophoresis
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Endothelin Receptor Antagonists
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Endothelins / pharmacology
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GRB2 Adaptor Protein
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GTP-Binding Proteins / physiology
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Mitogen-Activated Protein Kinase 1
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Peptide Fragments / pharmacology
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Peptides, Cyclic / pharmacology
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Pertussis Toxin
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Phosphorylation
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Protein Serine-Threonine Kinases / metabolism
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Protein-Tyrosine Kinases / pharmacology*
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Proteins / metabolism
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-raf
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Rats
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Receptor, Endothelin B
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Receptors, Endothelin / metabolism*
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Tyrosine / metabolism
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Virulence Factors, Bordetella / pharmacology
Substances
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Adaptor Proteins, Signal Transducing
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Endothelin Receptor Antagonists
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Endothelins
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GRB2 Adaptor Protein
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Grb2 protein, rat
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Peptide Fragments
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Peptides, Cyclic
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Proteins
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Proto-Oncogene Proteins
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Receptor, Endothelin B
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Receptors, Endothelin
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Virulence Factors, Bordetella
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sovateltide
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Tyrosine
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DNA
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Cyclic AMP
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Pertussis Toxin
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Protein-Tyrosine Kinases
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf
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Calcium-Calmodulin-Dependent Protein Kinases
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Mitogen-Activated Protein Kinase 1
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GTP-Binding Proteins
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cyclo(Trp-Asp-Pro-Val-Leu)