Lack of involvement of pertussis toxin-sensitive G-proteins in norepinephrine-induced vasoconstriction of rat aorta smooth muscle.
Several studies have shown that stimulation of pertussis toxin (PTX)-sensitive G-proteins amplified alpha-adrenoceptor (alpha-AR) agonist-induced vasoconstriction in small muscular and resistance arteries. The aim of this study was to assess the potential involvement of PTX-sensitive G-proteins in norepinephrine (NE)-induced constriction in a large diameter artery, the rat aorta. PTX (1 microg/mL, 2 hr; 3 microg/mL, 4 hr) did not modify concentration-response curves to NE in endothelium-denuded aortic rings. However, several lines of evidence suggested that aortic smooth muscle cells (SMC) had a PTX-sensitive G-protein pathway. [alpha-(32)P]ADP-ribosylation of G(i/o)-proteins by PTX (3 microg/mL, 4 hr) was demonstrated in situ in the intact aorta without endothelium. alpha(i/o) subunits were identified in vitro by both immunoblotting and ADP-ribosylation experiments in rat aorta SMC membranes. The measurement of G(i/o)-specific GTPase activity evidenced an effective coupling between NE receptors and G(i/o)-proteins, as NE induced an increase in basal G(i/o)-specific GTPase activity (20.7 +/- 2.8 vs 7.2 +/- 2.2 pmol P(i)/mg protein at 5 min; P < 0.05 vs basal). Co-immunoprecipitation revealed the in vitro coupling between alpha(1D)-ARs and G(i)-protein in rat aorta SMC membranes. In conclusion, we identified a PTX-sensitive G(i/o)-protein pathway in rat endothelium-denuded aorta. We showed an effective coupling between NE receptors and G(i)-proteins via alpha(1D)-ARs. Since PTX has no effect on NE-induced vasoconstriction, the PTX-sensitive G(i)-protein pathway does not play a predominant role in NE-induced responses in rat aorta SMC in contrast to small diameter muscular and resistance arteries.
Laboratoire de Neuroimmunologie et Inflammation, Centre de Recherche Public-Santé, L-1150, Luxembourg.
M A
MA
Petitcolin
C
C
Vandeputte
E
E
Spitzbarth-Régrigny
J L
JL
Bueb
C
C
Capdeville-Atkinson
E
E
Tschirhart
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000302:isolation & purification / Q000502:physiology*; D020962:Heterotrimeric GTP-Binding Proteins / Q000302:isolation & purification / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D037342:Pertussis Toxin; D011224:Prazosin / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000502:physiology; D018340:Receptors, Adrenergic, alpha-1 / Q000032:analysis; D014316:Tritium; D014661:Vasoconstriction / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; 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; D009638:Norepinephrine; D011224:Prazosin