ACh-induced relaxations of rabbit small mesenteric arteries: role of arachidonic acid metabolites and K⁺

Abstract

Zhang DX, Gauthier KM, Chawengsub Y, Campbell WB. ACh-induced relaxations of rabbit small mesenteric arteries: role of arachidonic acid metabolites and K ϩ . Am J Physiol Heart Circ Physiol 293: H152-H159, 2007. First published March 2, 2007; doi:10.1152/ajpheart.00268.2006.-ACh-induced endothelium-dependent relaxation in rabbit small mesenteric arteries is resistant to N-nitro-L-arginine (L-NA) and indomethacin but sensitive to high K ϩ , indicating the relaxations are mediated by endothelium-derived hyperpolarizing factors (EDHFs). The identity of the EDHFs in this vascular bed remains undefined. Small mesenteric arteries pretreated with L-NA and indomethacin were contracted with phenylephrine. ACh (10 Ϫ10 to 10 Ϫ6 M) caused concentration-dependent relaxations that were shifted to the right by lipoxygenase inhibition and the Ca 2ϩ -activated K ϩ channel inhibitors apamin (100 nM) or charybdotoxin (100 nM) and eliminated by the combination of apamin plus charybdotoxin. Relaxations to ACh were also blocked by a combination of barium (200 M) and apamin but not barium plus charybdotoxin. Addition of K ϩ (10.9 mM final concentration) to the preconstricted arteries elicited small relaxations. K ϩ addition before ACh restored the charybdotoxin-sensitive component of relaxations to ACh. K ϩ (10.9 mM) also relaxed endothelium-denuded arteries, and the relaxations were inhibited by barium but not by charybdotoxin and apamin. With the use of whole cell patch-clamp analysis, ACh (10 Ϫ7 M) stimulated voltage-dependent outward K ϩ current from endothelial cells, which was inhibited by charybdotoxin, indicating K ϩ efflux. Arachidonic acid (10 Ϫ7 to 10 Ϫ4 M) induced concentration-related relaxations that were inhibited by apamin but not by charybdotoxin and barium. Addition of arachidonic acid after K ϩ (10.9 mM) resulted in more potent relaxations to arachidonic acid compared with control without K ϩ (5.9 mM). These findings suggest that, in rabbit mesenteric arteries, ACh-induced, L-NA-and indomethacin-resistant relaxation is mediated by endothelial cell K ϩ efflux and arachidonic acid metabolites, and a synergism exists between these two separate mechanisms.acetylcholine; potassium channels; lipoxygenase; endothelium-derived hyperpolarizing factor STIMULATION OF THE VASCULAR endothelium with ACh, bradykinin, and increases in flow induces vasodilation by releasing soluble factors such as nitric oxide (NO), prostacyclin, and endothelium-derived hyperpolarizing factors (EDHFs; see Refs.

Endothelial 15-Lipoxygenase-1 Overexpression Increases Acetylcholine-Induced Hypotension and Vasorelaxation in Rabbits

“…THETAs are also EDHFs that are released on ACH stimulation, 4 activate the small conductance calciumdependent potassium channels, and hyperpolarize smooth muscle cells causing relaxations. 7 The maximum ACHinduced decrease in MAP was greater in Ad-15-LO-1-infected rabbits than normal or Ad-␤-Gal-infected rabbits. This indicates that 15-LO-1 overexpression contributed to ACH-induced hypotension, and this effect was not because of the viral infection.…”

“…5,6 However, 11,12,15-trihydroxyeicosatrienoic acid hyperpolarizes smooth muscle cells and relaxes rabbit aorta and mesenteric arteries (MAs). 3,4,7 Relaxations induced by 11,12,15-trihydroxyeicosatrienoic acid are inhibited by high K ϩ and calcium-dependent potassium-channel inhibitors. Therefore, 11,12,15-trihydroxyeicosatrienoic acid is an endothelium-derived hyperpolarizing factor (EDHF).…”

11(R),12(S),15(S)-trihydroxyeicosa-5(Z),8(Z),13(E)-trienoic acid: an endothelium-derived 15-lipoxygenase metabolite that relaxes rabbit aorta

“…These findings indicate that a portion of the endothelium-dependent relaxation is mediated by EDHF. The prostaglandin-and nitric oxide-independent relaxations to acetylcholine are inhibited by the SK Ca channel blocker apamin, high extracellular K ϩ , phospholipase inhibitors, and lipoxygenase inhibitors (3,12,20,27). They are also inhibited by antisense oligonucleotides against 15-LO, but not by scrambled oligonucleotides (26).…”

“…Epoxide hydrolase converts 15-H-11,12-EETA to 11,12,15-trihydroxyeicosatrienoic acid (11,12,. In isolated aortic smooth muscle cells, 11,12,15-THETA activates small-conductance K Ca (SK Ca ) channels, an effect blocked by apamin (3,12,27). In addition, 11,12,15-THETA hyperpolarizes smooth muscle cells and causes relaxation.…”

15-Lipoxygenase metabolites contribute to age-related reduction in acetylcholine-induced hypotension in rabbits

“…4, 11) and 15-lipoxygenase-1 (15-LO-1; Refs. 24,25) and the potassium (K) ion (9,36). AA metabolites of 15-LO-1, 11,12,15-trihydroxyeicosatrienoic acid (THETA) and 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA), are EDHFs (6) and mediate the ACh-induced relaxations in rabbit arteries in the presence of NO-and PG-synthesis inhibitors N -nitro-L-arginine (L-NNA) and indomethacin (Indo; Refs.…”