Zhao Z, Francis C E, Ravid K
Department of Biochemistry and Whitaker Cardiovascular Institute, Boston University School of Medicine, Massachusetts 02139, USA.
Microvasc Res. 1997 Nov;54(3):243-52. doi: 10.1006/mvre.1997.2044.
Adenosine analogs are known to induce changes in the steady-state concentration of cAMP via binding to adenylyl cyclase-inhibitory or -stimulatory adenosine receptors. Although adenosine has been found to increase cAMP in vascular smooth muscle cells (VSMC), we found by the polymerase chain reaction of reverse-transcribed RNA and subsequently by Northern blot analysis that rat VSMC express high levels of an A3-subtype adenosine receptor cDNA which encodes an adenylyl cyclase-inhibitory adenosine receptor. The A3-specific agonist, N6-(3-iodobenzyl) adenosine-5'-N-mehylcarboxamide (IB-MECA) indeed decreases cAMP levels in VSMC cultured in the presence of forskolin. Antisense oligomers to the A3 adenosine receptor significantly reduce the level of this receptor in VSMC and potentiate endogenous adenosine- or 5'-N-ethylcarboxamido adenosine-induced increases in cAMP and of the proto-oncogene c-fos. Abrogating the expression of the A3 adenosine receptor also largely abolishes IB-MECA-induced inhibition of adenylyl cyclase. The level of A3 adenosine receptor mRNA and the extent of changes in cAMP in response to IB-MECA were lower in cultures of VSMC derived from adult rats, compared to VSMC from neonatal rats. The expression of a functional A3 adenosine receptor was also confirmed in preparations of isolated aortas. Our findings thus indicate that: (a) the A3-type receptor is a functional inhibitory adenosine receptor in VSMC; and (b) the regulation of expression of the A3 receptor is critical in determining effects of adenosine on the steady-state concentration of cAMP.
已知腺苷类似物通过与腺苷酸环化酶抑制性或刺激性腺苷受体结合，诱导环磷酸腺苷（cAMP）稳态浓度的变化。尽管已发现腺苷可增加血管平滑肌细胞（VSMC）中的cAMP，但我们通过逆转录RNA的聚合酶链反应以及随后的Northern印迹分析发现，大鼠VSMC表达高水平的A3亚型腺苷受体cDNA，该cDNA编码一种腺苷酸环化酶抑制性腺苷受体。A3特异性激动剂N6-（3-碘苄基）腺苷-5'-N-甲基羧酰胺（IB-MECA）确实可降低在福司可林存在下培养的VSMC中的cAMP水平。针对A3腺苷受体的反义寡聚物可显著降低VSMC中该受体的水平，并增强内源性腺苷或5'-N-乙基羧酰胺腺苷诱导的cAMP和原癌基因c-fos的增加。消除A3腺苷受体的表达也可在很大程度上消除IB-MECA诱导的腺苷酸环化酶抑制作用。与新生大鼠的VSMC相比，成年大鼠来源的VSMC培养物中A3腺苷受体mRNA的水平以及对IB-MECA反应的cAMP变化程度较低。在离体主动脉制剂中也证实了功能性A3腺苷受体的表达。因此，我们的研究结果表明：（a）A3型受体是VSMC中的一种功能性抑制性腺苷受体；（b）A3受体表达的调节对于确定腺苷对cAMP稳态浓度的影响至关重要。
