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-deri ved hyperpolarizing factor (EDHF) (sensitive to high-external K+ and apamin e) production by the vascular endothelium leading to dilation. We hypothesi zed that alpha- and beta gamma -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/II)-subunits abolished acetylcholine (Ach)-medi ated dilation but failed to influence oxymetazoline (Oxy, alpha (2)-adrener gic receptor agonist)-induced dilation. In contrast, alpha (il-2)-subunit A bs prevented Oxy- but not Ach-induced dilation. Thus, as expected, endothel ial 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)-sen sitive component but did not impair the high-external K+-sensitive componen t of the dilation induced by Ach and Oxy. Thus, G protein P-subunits primar ily accounted for NO production. Neutralization of Hsp90 and inhibition of the phospholipase C by U73122 (1 mu mol/L) or intracellular Ca2+ buffering with BAPTA-AM (10 mu mol/L) sharply reduced NO-dependent but not K+-sensiti ve 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 dilati on was insensitive to beta -subunit Abs. Although not directly activating t he NO pathway, alpha -subunit activation is an absolute prerequisite for re ceptor-operated endothelium-dependent dilation of resistance arteries.