Hosey M M, McMahon K K, Green R D
J Mol Cell Cardiol. 1984 Oct;16(10):931-42. doi: 10.1016/s0022-2828(84)80029-2.
Adenosine causes negative chronotropic and inotropic effects on cardiac tissue. We have investigated the nature of the cardiac adenosine receptor and its effector mechanisms in preparations of newborn chick heart. The adenosine analog [3H]N6 (L-phenylisopropyl) adenosine (L-PIA), an agonist at R-type adenosine receptors, bound with high affinity to receptors in crude and highly-purified membrane preparations. The KD was 3-5 nM. The receptor density was low in crude membranes (10 fmol/mg protein) but significantly enriched in purified sarcolemma (164 fmol/mg protein). Competition studies showed that N-ethylcarboxamide adenosine and N6(D-phenylisopropyl)adenosine were less potent than N6(L-phenylisopropyl)adenosine at the chick heart adenosine receptor, as expected for an Ri-type adenosine receptor. Gpp(NH)p decreased the binding of [3H]N6(L-phenylisopropyl)adenosine to chick heart membranes, suggesting that the guanine nucleotide converted the receptor to a lower affinity state. N6(L-phenylisopropyl)adenosine inhibited beta-adrenergic receptor stimulated adenylate cyclase activity. The IC50 for cyclase attenuation by N6(L-phenylisopropyl)adenosine was 1 microM. N6(L-phenylisopropyl)adenosine reversed the effect of the beta-receptor agonist isoproterenol on phospholamban phosphorylation in 32P-labelled slices of newborn chick hearts. This effect of N6(L-phenylisopropyl)adenosine was evident by 2 min, had an IC50 of 200 nM, and was prevented by the adenosine receptor antagonist 8-phenyltheophylline. Taken together, the results suggest that the antiadrenergic effects of adenosine on cardiac tissue are mediated by a decrease in membrane protein phosphorylation signalled by activation of Ri-adenosine receptors. The coupling mechanism between receptor activation and protein phosphorylation may be an attenuation of adenylate cyclase.
腺苷对心脏组织具有负性变时和变力作用。我们在新生雏鸡心脏标本中研究了心脏腺苷受体的性质及其效应机制。腺苷类似物[3H]N6（L-苯异丙基）腺苷（L-PIA）是R型腺苷受体的激动剂，它与粗制和高度纯化的膜制剂中的受体具有高亲和力结合。解离常数（KD）为3 - 5 nM。粗制膜中的受体密度较低（10 fmol/mg蛋白），但在纯化的肌膜中显著富集（164 fmol/mg蛋白）。竞争研究表明，N-乙基羧酰胺腺苷和N6（D-苯异丙基）腺苷在雏鸡心脏腺苷受体上的效力低于N6（L-苯异丙基）腺苷，这与Ri型腺苷受体的预期相符。鸟苷-5'-O-（3-硫代三磷酸）（Gpp(NH)p）降低了[3H]N6（L-苯异丙基）腺苷与雏鸡心脏膜的结合，表明鸟嘌呤核苷酸将受体转变为低亲和力状态。N6（L-苯异丙基）腺苷抑制β-肾上腺素能受体刺激的腺苷酸环化酶活性。N6（L-苯异丙基）腺苷使腺苷酸环化酶衰减的半数抑制浓度（IC50）为1 μM。N6（L-苯异丙基）腺苷逆转了β受体激动剂异丙肾上腺素对新生雏鸡心脏32P标记切片中受磷蛋白磷酸化的作用。N6（L-苯异丙基）腺苷的这种作用在2分钟时明显，IC50为200 nM，并且被腺苷受体拮抗剂8-苯基茶碱所阻断。综上所述，结果表明腺苷对心脏组织的抗肾上腺素能作用是由Ri-腺苷受体激活所引发的膜蛋白磷酸化减少介导的。受体激活与蛋白磷酸化之间的偶联机制可能是腺苷酸环化酶衰减。
