Marsh J D, Lachance D, Kim D
Circ Res. 1985 Jul;57(1):171-81. doi: 10.1161/01.res.57.1.171.
To examine mechanisms by which cardiac tissue regulates the beta-adrenergic receptor and physiological response to beta-adrenergic agonists, we studied the effects of cytoskeletal disrupting agents and inhibition of protein synthesis on receptor properties and contractile response to isoproterenol in intact cultured ventricular cells from embryonic chick heart. Thirty minutes of exposure of intact cells to 1 microM isoproterenol produced loss of the high-affinity state (KD = 4.5 +/- 1.5 nM) of the receptor found in cell membranes with no loss of total receptor number, whereas there was concomitant decline in the contractile response to 1 microM isoproterenol to 41 +/- 16% (SD) of control. Contractile response recovered within 60 minutes of agonist removal to 78 +/- 11% of initial response. There was concomitant recovery of the high-affinity state of the receptor, so that 1 hour after agonist removal there was 72% of the initial proportion of high-affinity receptors. This desensitization of the contractile response, as well as recovery after agonist removal, was markedly blunted by preincubation with cytochalasin B so that contractile responsiveness to isoproterenol was maintained at 77 +/- 13% of the initial response. Colchicine (10 microM) was without effect on the first 30 minutes of agonist-induced desensitization. More prolonged agonist exposure (1 microM isoproterenol for 24 hours) produced colchicine-sensitive loss of receptors from intact cells to 40% of control levels. Full recovery of receptor number occurred over 72 hours; this was completely blocked by cycloheximide (P less than 0.01). Thus, rapid desensitization and resensitization of the beta-receptor-mediated contractile response is associated with alterations in high-affinity agonist binding and appears to be modulated by microfilaments. Receptor down-regulation is dependent on functional microtubules, and recovery of these receptors after agonist removal requires protein synthesis.
为了研究心脏组织调节β-肾上腺素能受体的机制以及对β-肾上腺素能激动剂的生理反应，我们研究了细胞骨架破坏剂和蛋白质合成抑制对来自胚胎鸡心脏的完整培养心室细胞中受体特性和对异丙肾上腺素收缩反应的影响。完整细胞暴露于1微摩尔/升异丙肾上腺素30分钟后，细胞膜中发现的受体高亲和力状态（KD = 4.5 +/- 1.5纳摩尔）丧失，而总受体数量未减少，同时对1微摩尔/升异丙肾上腺素的收缩反应下降至对照的41 +/- 16%（标准差）。激动剂去除后60分钟内，收缩反应恢复至初始反应的78 +/- 11%。受体的高亲和力状态也随之恢复，因此激动剂去除1小时后，高亲和力受体的初始比例为72%。用细胞松弛素B预孵育可显著减弱这种收缩反应的脱敏以及激动剂去除后的恢复，从而使对异丙肾上腺素的收缩反应性维持在初始反应的77 +/- 13%。秋水仙碱（10微摩尔/升）对激动剂诱导的脱敏的前30分钟没有影响。更长时间的激动剂暴露（1微摩尔/升异丙肾上腺素处理24小时）导致完整细胞中受体数量出现秋水仙碱敏感的减少，降至对照水平的40%。受体数量在72小时内完全恢复；这被环己酰亚胺完全阻断（P小于0.01）。因此，β受体介导的收缩反应的快速脱敏和再敏化与高亲和力激动剂结合的改变有关，并且似乎受到微丝的调节。受体下调依赖于功能性微管，激动剂去除后这些受体的恢复需要蛋白质合成。
