Relationship between α₁-Adrenergic Receptor-Induced Contraction and Extracellular Signal-Regulated Kinase Activation in the Bovine Inferior Alveolar Artery

Abstract

The endogenous adrenergic agonists norepinephrine (NE) and epinephrine regulate vascular tone by stimulating ␣ 1 -adrenergic receptors (ARs) on smooth muscle cells to cause contraction. In addition, ␣ 1 -ARs also couple to growth factor pathways, through stimulation of mitogen-activated protein kinases (MAPKs). MAPKs are a family of serine-threonine kinases that include extracellular signal-regulated kinase (ERK) and a variety of other kinases that are able to activate transcription factors when stimulated. We examined ␣ 1 -AR stimulation of contraction and ERK activation in the bovine inferior alveolar artery (BIAA), using in vitro contraction studies and Western blotting. Using antagonists selective for individual adrenergic receptor types, we found that only ␣ 1 -ARs were coupled to ERK activation and contraction. NE stimulated contraction (EC 50 ϭ 11 M) and ERK activation (EC 50 ϭ 21 M) with similar potency. Using ␣ 1 -AR subtype-selective antagonists, we identified the ␣ 1 -AR subtypes coupled to each response. Affinity values for ␣ 1 -AR subtype-selective antagonists were consistent with ␣ 1A -AR-mediated contraction. In contrast, simultaneous treatment with concentrations of these antagonists selective for each ␣ 1 -AR subtype (␣ 1A -, ␣ 1B -, and ␣ 1D -AR) was required to inhibit ERK activation, suggesting that all three ␣ 1 -ARs activate ERK in BIAA. Transmural electrical stimulation of BIAA segments resulted in activation of ERK, which was inhibited by the ␣ 1 -ARselective antagonist BE 2254 (2-[[␤-(4-hydroxyphenyl)ethyl]aminomethyl]-1-tetralone). These data suggest that in an intact artery, NE released from sympathetic nerves stimulates ␣ 1 -ARs to cause contraction and ERK activation, and that redundancy among subtypes exists for ␣ 1 -AR activation of ERK.The sympathetic nervous system controls peripheral vascular resistance by release of norepinephrine (NE) and epinephrine, which stimulate ␣ 1 -adrenergic receptors (ARs) on vascular smooth muscle cells. Molecular cloning and radioligand binding studies using selective antagonists have identified three distinct ␣ 1 -AR subtypes (␣ 1A -, ␣ 1B -, and ␣ 1D -AR).

Extracellular Signal-Regulated Kinase (ERK1/2) Contributes to Endotoxin-Induced Hyporeactivity via Nitric Oxide and Prostacyclin Production in Rat Aorta

“…Additionally, several studies suggest that ERK1/2 phosphorylation by norepinephrine may play a role in the regulation of contraction in intact vascular preparations [17,21,23,28,44] , whereas others suggest it may not [22,24] . In the present study, a specific inhibitor of ERK1/2 phosphorylation by MEK1/2, U0126, at 1 and 10 g/ml concentrations, caused a further decrease in the E max value of norepinephrine.…”

“…Although ERK activation is generally involved in the regulation of gene expression via phosphorylation of transcription factors, protein synthesis and the activation of cytoplasmic and membrane proteins [16] , this pathway has also been shown to play an important role in vascular smooth muscle contraction under calcium-dependent and calciumindependent conditions [17][18][19][20] . It has been demonstrated that the MEK1/2-ERK1/2 pathway is involved in the vasoconstriction induced by G-protein-coupled agonists, such as norepinephrine, angiotensin II or 5-hydroxytryptamine [21][22][23][24] . Involvement of MAPKs including ERK1/2 has also been reported in the endotoxin-induced cellular responses, such as the increased activity of iNOS [25] .…”

Transactivation of Epidermal Growth Factor Receptor Mediates Catecholamine-Induced Growth of Vascular Smooth Muscle

“…Similar to non-GPCR growth factor RTKs such as the epidermal growth factor receptor (EGFR), several GPCRs signal growth factor-like activity through one or more of these MAPK cascades. 13 Although ␣ 1 -AR stimulation has been shown to activate ERK1/2 (also denoted p42/p44 MAPK) in cultured SMCs, 4,14,15 no studies have determined which MAPK pathways are required for ␣ 1 -AR-induced growth in the intact artery.…”

Characterization of the α1-adrenoceptor subtype activating extracellular signal-regulated kinase in submandibular gland acinar cells

“…ERK1/2 activity was measured using a modification of the method described by Hague et al (2002). ERK1/2 activity was stopped by rapid aspiration of the incubation solution followed with addition of ice-cold lysis buffer containing 137 mM NaCl, 20 mM Tris HCl, 1 mM CaCl 2 , 1 mM MgCl 2 , 1% Nonidet P-40, 1 mM EDTA, 1 μM aprotinin, 100 μM phenylmethylsulfonyl fluoride, and 10 nM okadaic acid (Sigma-Aldrich).…”

“…All three of the α 1 -adrenoceptor subtypes have been shown to couple to ERK1/2 activation in a variety of cell types (Zhong and Minneman, 1999;Hague et al, 2002;Jiao et al, 2002), although the physiological functions of this pathway are not well understood. Recently, Huang et al (2007) reported in cardiomyocytes that α 1 -adrenoceptors activate an anti-apoptotic, cell survival pathway by stimulation of ERK 1/2.…”