Prentice D J, Hourani S M
School of Biological Sciences, University of Surrey, Guildford, UK.
Naunyn Schmiedebergs Arch Pharmacol. 2000 Nov;362(4-5):427-34. doi: 10.1007/s002100000292.
The aim of this study was to characterise the receptor(s) mediating relaxations to adenosine and its analogues in the hamster isolated aorta. Adenosine relaxed the aorta but there was no significant difference between pIC20 values in the absence and presence of 8-sulphophenyltheophylline (8-SPT, 50 microM), although there was a small right-shift (approximately threefold) of the lower portion of the curve in the presence of 8-SPT. However, in the presence of the adenosine uptake inhibitor nitrobenzylthioinosine (NBTI, 1 microM), curves to adenosine were left-shifted by approximately 100-fold and an apparent pK(B) for 8-SPT of 5.79+/-0.05 was obtained. Likewise, 5'-N-ethylcarboxamidoadenosine (NECA) relaxed the aorta but curves were biphasic. The first phase of the curve was blocked by 8-SPT (10-100 microM, pA2 = 5.75+/-0.14) and the A2A-selective antagonist 4-(2-[7-amino-2-(2-furyl) [1,2,4]-triazolo[2,3-a][1,3,5]triazin-5-ylaminolethyl) phenol (ZM 241385, 3 nM-1 microM, pK(B)=9.17+/-0.10). Similarly, the A2A-selective agonist 2-[p)-(2-carbonylethyl)-phenylethylamino]-5'-N-ethylcarboxam idoadenosine (CGS 21680) relaxed the tissues but curves were biphasic and the first phase was again blocked by ZM 241385 (10 nM, apparent pK(B)=9.06+/-0.34). In contrast, relaxations to N6-R-phenylisopropyladenosine (R-PIA), N6-cyclopentyladenosine (CPA), 2-chloroadenosine (2-CADO) and N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) were not blocked by 8-SPT (50 microM). Responses to IB-MECA were also not blocked by the A3 receptor antagonist 3-ethyl-5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1,4-(+/-)-dihyd ropyridine-3,5-dicarboxylate (MRS 1191, 30 microM). The asymptote of the first phase of curves to NECA was markedly reduced (and in some preparations the first phase was completely abolished) both in the presence of N(G)-nitro-L-arginine methyl ester (L-NAME, 0.1 mM), and in the absence of endothelium. Likewise, the first phase of curves to CGS 21680 was abolished both in the presence of L-NAME (0.1 mM) and in the absence of endothelium. In contrast, there were only relatively small shifts to the right of curves to adenosine and the other analogues in the presence of L-NAME or the absence of endothelium (between three- and fivefold). The data suggest the presence of A2A receptors which are located on the endothelium and mediate release of nitric oxide. These receptors are activated by NECA, CGS 21680 and adenosine (in the presence of uptake blockade). The resistance to blockade of relaxations to adenosine (in the absence of uptake inhibitor), CPA, R-PIA, 2-CADO, IB-MECA and high concentrations of NECA and CGS 21680 by 8-SPT or ZM 241385 suggests the presence of an additional mechanism(s). Data obtained with adenosine in the absence and presence of NBTI suggest that the endogenous ligand may cause relaxation via an intracellular mechanism.
本研究的目的是鉴定介导仓鼠离体主动脉对腺苷及其类似物舒张反应的受体。腺苷可使主动脉舒张，但在不存在和存在8 - 磺基苯基茶碱（8 - SPT，50 μM）的情况下，pIC20值无显著差异，尽管在存在8 - SPT时曲线下部有小的右移（约三倍）。然而，在存在腺苷摄取抑制剂硝基苄硫基肌苷（NBTI，1 μM）的情况下，腺苷曲线左移约100倍，得到8 - SPT的表观pK(B)为5.79±0.05。同样，5'-N - 乙基甲酰胺基腺苷（NECA）可使主动脉舒张，但曲线呈双相。曲线的第一相被8 - SPT（10 - 100 μM，pA2 = 5.75±0.14）和A2A选择性拮抗剂4 - (2 - [7 - 氨基 - 2 - (2 - 呋喃基)[1,2,4] - 三唑并[2,3 - a][1,3,5]三嗪 - 5 - 基氨基乙基)苯酚（ZM 241385，3 nM - 1 μM，pK(B)=9.17±0.10）阻断。类似地，A2A选择性激动剂2 - [p - (2 - 羰基乙基) - 苯乙氨基] - 5'-N - 乙基甲酰胺基腺苷（CGS 21680）可使组织舒张，但曲线呈双相，第一相再次被ZM 241385（10 nM，表观pK(B)=9.06±0.34）阻断。相比之下，对N6 - R - 苯基异丙基腺苷（R - PIA）、N6 - 环戊基腺苷（CPA）、2 - 氯腺苷（2 - CADO）和N6 - (3 - 碘苄基) - 腺苷 - 5'-N - 甲基脲苷（IB - MECA）的舒张反应未被8 - SPT（50 μM）阻断。对IB - MECA的反应也未被A3受体拮抗剂3 - 乙基 - 5 - 苄基 - 2 - 甲基 - 6 - 苯基 - 4 - 苯乙炔基 - 1,4 - (±) - 二氢吡啶 - 3,5 - 二羧酸酯（MRS 1191，30 μM）阻断。在存在N(G) - 硝基 - L - 精氨酸甲酯（L - NAME，0.1 mM）时以及无内皮情况下，NECA曲线第一相的渐近线显著降低（在某些标本中第一相完全消失）。同样，在存在L - NAME（0.1 mM）和无内皮情况下，CGS 21680曲线的第一相消失。相比之下，在存在L - NAME或无内皮情况下，腺苷和其他类似物的曲线仅向右有相对较小的移动（三到五倍）。数据表明存在位于内皮上并介导一氧化氮释放的A2A受体。这些受体被NECA、CGS 21680和腺苷（在存在摄取阻断的情况下）激活。8 - SPT或ZM 241385对腺苷（在无摄取抑制剂时）、CPA、R - PIA、2 - CADO、IB - MECA以及高浓度NECA和CGS 21680舒张反应的阻断具有抗性，提示存在其他机制。在不存在和存在NBTI时用腺苷获得的数据表明内源性配体可能通过细胞内机制引起舒张。
