Endothelial G protein beta-subunits trigger nitric oxide-but not endothelium-derived hyperpolarizing factor-dependent dilation in rabbit resistance arteries.
A single subtype of heterotrimeric G protein-coupled receptor controls both nitric oxide (NO) (sensitive to L-arginine analogues) and endothelium-derived hyperpolarizing factor (EDHF) (sensitive to high-external K(+) and apamine) production by the vascular endothelium leading to dilation. We hypothesized that alpha- and betagamma-subunits of the G protein serve as distinct intermediates to produce NO and EDHF. In pressurized resistance arteries, selective pinocytotic endothelial incorporation of specific antibodies (Abs) directed against alpha(q/11)-subunits abolished acetylcholine (Ach)-mediated dilation but failed to influence oxymetazoline (Oxy, alpha(2)-adrenergic receptor agonist)-induced dilation. In contrast, alpha(i1-2)-subunit Abs prevented Oxy- but not Ach-induced dilation. Thus, as expected, endothelial muscarinic and alpha(2)-adrenoceptors couple to G(q) protein and G(i) proteins, respectively. beta-subunit Abs reduced both Ach- and Oxy-induced dilation. The beta-subunit Abs abolished the nitro-L-arginine (L-NNA)-sensitive component but did not impair the high-external K(+)-sensitive component of the dilation induced by Ach and Oxy. Thus, G protein beta-subunits primarily accounted for NO production. Neutralization of Hsp90 and inhibition of the phospholipase C by U73122 (1 micromol/L) or intracellular Ca(2+) buffering with BAPTA-AM (10 micromol/L) sharply reduced NO-dependent but not K(+)-sensitive dilation. In conclusion, mobilization of the G protein beta-subunit is pivotal to NO-dependent dilation triggered through muscarinic and alpha(2)-adrenergic receptors. In contrast, receptor-operated EDHF-dependent dilation was insensitive to beta-subunit Abs. Although not directly activating the NO pathway, alpha-subunit activation is an absolute prerequisite for receptor-operated endothelium-dependent dilation of resistance arteries.
Véquaud
P
P
Institut de Cardiologie de Montréal, Centre de Recherche, Montréal, Québec, Canada.
Thorin
E
E
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001685:Biological Factors / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D021122:Protein Subunits; D011817:Rabbits; D010738:Type C Phospholipases / Q000378:metabolism; D014655:Vascular Resistance / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D000906:Antibodies; D001685:Biological Factors; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D021122:Protein Subunits; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; D009569:Nitric Oxide; D010738:Type C Phospholipases; D020962:Heterotrimeric GTP-Binding Proteins; D002118:Calcium