Ungerer M, Kessebohm K, Kronsbein K, Lohse M J, Richardt G
1. Medizinische Klinik, Technischen Universität München, Germany.
Circ Res. 1996 Sep;79(3):455-60. doi: 10.1161/01.res.79.3.455.
During myocardial ischemia, a local release of noradrenaline coincides with an increased density of beta-adrenergic receptors. The functional activity of these receptors, however, is mainly determined by their state of phosphorylation. The beta-adrenergic receptor kinase (beta ARK) specifically phosphorylates and thereby inactivates beta-adrenergic receptors after stimulation by receptor agonists, facilitating the binding of the inhibitor protein beta-arrestin to the receptors. beta ARK activation involves a translocation of the enzyme to the membrane. In the present study, we investigated the density and the functional activity of beta-adrenergic receptors, the enzymatic activity of beta ARK in membranes and cytosol, the mRNA levels of beta ARK-1, and the expression of beta-arrestin during stop-flow and low-flow ischemia in the isolated perfused rat heart. After 60 minutes of stop-flow ischemia, beta-adrenergic receptor density was upregulated, but beta-agonist-mediated adenylate cyclase activity was blunted. Simultaneously, beta ARK activity in the particulate fraction was significantly induced. The increase in beta ARK activity was reversible after inhibition of ischemia-evoked noradrenaline release by desipramine. Also, exposure to externally given noradrenaline increased beta ARK activity in the particulate fraction. Cytosolic beta ARK activity remained largely unchanged during stop-flow or low-flow ischemia. The steady state concentration of beta ARK-1 mRNA increased after 20 minutes of stop-flow ischemia and then returned to baseline values after another 20 minutes. Cardiac ischemia did not alter beta-arrestin levels. During myocardial ischemia, an increase in the number of beta-adrenergic receptors is paralleled by increased membrane activity of the receptor kinase beta ARK. This increased membrane activity may contribute to enhanced receptor phosphorylation and inactivation.
在心肌缺血期间，去甲肾上腺素的局部释放与β-肾上腺素能受体密度的增加同时出现。然而，这些受体的功能活性主要由其磷酸化状态决定。β-肾上腺素能受体激酶（βARK）在受体激动剂刺激后特异性地使β-肾上腺素能受体磷酸化，从而使其失活，促进抑制蛋白β-抑制蛋白与受体的结合。βARK的激活涉及该酶向膜的转位。在本研究中，我们调查了离体灌注大鼠心脏在停流和低流量缺血期间β-肾上腺素能受体的密度和功能活性、膜和胞质溶胶中βARK的酶活性、βARK-1的mRNA水平以及β-抑制蛋白的表达。停流缺血60分钟后，β-肾上腺素能受体密度上调，但β-激动剂介导的腺苷酸环化酶活性减弱。同时，微粒体部分的βARK活性显著诱导。在用去甲丙咪嗪抑制缺血诱发的去甲肾上腺素释放后，βARK活性的增加是可逆的。此外，暴露于外源性给予的去甲肾上腺素会增加微粒体部分的βARK活性。在停流或低流量缺血期间，胞质溶胶中的βARK活性基本保持不变。停流缺血20分钟后，βARK-1 mRNA的稳态浓度升高，然后在另外20分钟后恢复到基线值。心脏缺血并未改变β-抑制蛋白水平。在心肌缺血期间，β-肾上腺素能受体数量的增加与受体激酶βARK的膜活性增加同时出现。这种增加的膜活性可能有助于增强受体的磷酸化和失活。
