title: Role of G(i)-proteins in norepinephrine-mediated vasoconstriction in rat tail artery smooth muscle.
abstract: We showed, in rat de-endothelialised tail artery, that pertussis toxin (PTX) (1 microg/mL, 2 hr) attenuated norepinephrine (NE)-induced vasoconstriction without modifying intracellular calcium concentration [Ca2+](i) mobilisation. We suggested the existence of two NE-induced intracellular pathways: a first, which would be insensitive to PTX and lead to [Ca2+](i) mobilisation, and a second sensitive to PTX and involved in the [Ca2+](i) sensitivity of NE-induced contraction. The aim of this study was to demonstrate the existence of the second intracellular pathway. PTX-sensitive G(i/o)-proteins in rat tail artery SMC membrane were identified by immunoblot and ADP-ribosylation. [(32)P]ADP-ribosylation of alpha(i/o)-subunits was demonstrated in situ by perfusing rat de-endothelialised tail artery segments with PTX (1 microg/mL, 2 hr), which suggested that G(i/o)-protein inactivation was involved in the reduction by PTX of the [Ca2+](i) sensitivity of NE-induced contraction. Coupling between G(i/o)-proteins and NE receptors was confirmed by the NE-induced increase in G(i/o)-specific GTPase activity (24.1 +/- 1.9 vs 8.8 +/- 0.4 pmol P(i)/mg protein at 5 min; P < 0.05 vs basal). [(3)H]Prazosin-binding data showed the presence of a heterogeneous alpha(1)-AR population in rat tail artery smooth muscle cells. We demonstrated the in vitro coupling between alpha(1A)-AR subtype and alpha(i)-subunits. In conclusion, we identified, in rat de-endothelialised tail artery, a PTX-sensitive G(i/o)-protein-modulated pathway that is coupled to NE receptors via alpha(1A)-AR. We suggest that NE stimulates two alpha(1)-AR-mediated intracellular pathways: a first, which is mediated by a G(q)-protein and leads to [Ca2+](i) mobilisation and contraction, and a second, which is mediated by a G(i)-protein and is involved in the amplification of the [Ca2+](i) sensitivity of NE-induced tension.
authors: Laboratoire de Neuroimmunologie et Inflammation, Centre de Recherche Public-Santé, L-1150 Luxembourg, Luxembourg.
authors: M A
authors: MA
authors: Petitcolin
authors: E
authors: E
authors: Spitzbarth-Régrigny
authors: J L
authors: JL
authors: Bueb
authors: C
authors: C
authors: Capdeville-Atkinson
authors: E
authors: E
authors: Tschirhart
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001158:Arteries / Q000166:cytology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism / Q000502:physiology*; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000502:physiology*; D037342:Pertussis Toxin; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000378:metabolism; D018340:Receptors, Adrenergic, alpha-1 / Q000032:analysis; D015398:Signal Transduction; D013623:Tail; D014316:Tritium; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D011941:Receptors, Adrenergic; D018340:Receptors, Adrenergic, alpha-1; D010566:Virulence Factors, Bordetella; D014316:Tritium; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin