Biochemical and functional characterization of high-affinity urotensin II receptors in rat cortical astrocytes.
The urotensin II (UII) gene is primarily expressed in the central nervous system, but the functions of UII in the brain remain elusive. Here, we show that cultured rat astrocytes constitutively express the UII receptor (UT). Saturation and competition experiments performed with iodinated rat UII ([(125)I]rUII) revealed the presence of high- and low-affinity binding sites on astrocytes. Human UII (hUII) and the two highly active agonists hUII(4-11) and [3-iodo-Tyr9]hUII(4-11) were also very potent in displacing [(125)I]rUII from its binding sites, whereas the non-cyclic analogue [Ser5,10]hUII(4-11) and somatostatin-14 could only displace [(125)I]rUII binding at micromolar concentrations. Reciprocally, rUII failed to compete with [(125)I-Tyr0,D-Trp8]somatostatin-14 binding on astrocytes. Exposure of cultured astrocytes to rUII stimulated [(3)H]inositol incorporation and increased intracellular Ca(2+) concentration in a dose-dependent manner. The stimulatory effect of rUII on polyphosphoinositide turnover was abolished by the phospholipase C inhibitor U73122, but only reduced by 56% by pertussis toxin. The GTP analogue Gpp(NH)p caused its own biphasic displacement of [(125)I]rUII binding and provoked an affinity shift of the competition curve of rUII. Pertussis toxin shifted the competition curve towards a single lower affinity state. Taken together, these data demonstrate that rat astrocytes express high- and low-affinity UII binding sites coupled to G proteins, the high-affinity receptor exhibiting the same pharmacological and functional characteristics as UT.
Castel
Hélène
H
INSERM, Laboratory of Cellular and Molecular Neuroendocrinology, European Institute for Peptide Research, University of Rouen, Mont-Saint-Aignan, France.
Diallo
Mickaël
M
Chatenet
David
D
Leprince
Jérôme
J
Desrues
Laurence
L
Schouft
Marie-Thérèse
MT
Fontaine
Marc
M
Dubessy
Christophe
C
Lihrmann
Isabelle
I
Scalbert
Elisabeth
E
Malagon
Maria
M
Vaudry
Hubert
H
Tonon
Marie-Christine
MC
Gandolfo
Pierrick
P
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007294:Inositol / Q000378:metabolism; D007457:Iodine Radioisotopes; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014579:Urotensins / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007457:Iodine Radioisotopes; D018129:Phosphatidylinositol Phosphates; D043562:Receptors, G-Protein-Coupled; D014579:Urotensins; C473142:Uts2r protein, rat; D007294:Inositol; D006160:Guanosine Triphosphate; C029677:urotensin II; D010738:Type C Phospholipases; D002118:Calcium