beta-Adrenergic-sensitive adenylate cyclase in choroid plexus: properties and cellular localization.
beta-Adrenergic-sensitive adenylate cyclase in choroid plexus: properties and cellular localization.
复制标题
脉络丛中β-肾上腺素敏感的腺苷酸环化酶：特性和细胞定位。
作者：
J. Nathanson
由于生理证据表明肾上腺素能调节脉络丛分泌的可能性，本研究对猫脉络丛破碎细胞标本中β-肾上腺素能刺激的腺苷酸环化酶进行了详细的研究。该酶为GTP(EC50=2×10-6M)，但不依赖钙，可被低浓度的异丙肾上腺素(KA=1.4×10-7M)激活。在有镁离子存在的情况下，异丙肾上腺素增加了最大反应速度，但不改变对ATP的Km。添加镁/三磷酸腺苷的最佳比例为4~8/1。Mn2+和Co2+对酶活力也有一定的支持作用，而Cu2+对酶活性的影响较小。在受体激动剂中，异丙肾上腺素的作用最强，其次是肾上腺素(Ka=1.6×10~(-6)M)、去甲肾上腺素(Ka=2.5×10~(-5)M)、苯肾上腺素(Ka&Gt；2.5×10~(-5)M)和多巴胺(Ka=2×10~(-4)M)。低浓度(±)心得安(Ki=2.7×10~(-9)M)可阻断异丙肾上腺素的激活，而高浓度(+)心得安(Ki=3×10~(-6)M)、氟奋乃静(Ki=1.2×10~(-7)M)或酚妥拉明(Ki>；10~(-3)M)可阻断异丙肾上腺素的激活。在更具选择性的β肾上腺素能药物中，相对β2选择性的激动剂zinterol(Ka=2.3×10-8M)和OPC2009(Ka=1.3×10-7M)比β1的选择性激动剂丙二醇强得多。沙丁胺醇、特布他林和奥昔洛林的药效中等，与津替洛尔一起作为部分激动剂。在几种拮抗剂(IPS339、H35/25、丁毒胺、美托洛尔、对氧心痛、阿替洛尔和心得安)中，计算的抑制常数与相同药物阻断异丙肾上腺素刺激的腺苷环化酶和肺内IHYP结合的抑制常数有很好的相关性。激动剂和拮抗剂数据均表明脉络丛中与腺苷环化酶相关的β受体主要为β-2。解剖学研究表明，第四脑室的β肾上腺素能敏感的腺苷环化酶活性高于侧脑室脉络丛。细胞分离实验，利用几种不同的程序，一致地证明，与血管成分相比，在富含上皮细胞的部分中，激素敏感性显著增加。提示脉络丛分泌上皮可能存在β-2-肾上腺素能调节。
Because of physiological evidence suggesting the possibility of adrenergic regulation of choroid plexus secretion, a detailed study was undertaken to identify, characterize, and localize β-adrenergic-stimulated adenylate cyclase in broken cell preparations of cat choroid plexus. The enzyme was GTP (EC50 = 2 x 10-6 M)-but not calcium-dependent and was activated by low concentrations of isoproterenol (Ka = 1.4 x 10-7 M). Isoproterenol, in the presence of Mg2+, increased the maximal reaction velocity without altering the Km for ATP. The optimal ratio of added Mg2+/ATP was 4-8/1. Mn2+ and, to a lesser extent, Co2+ (but not Cu2+) could also support enzyme activity. Among receptor agonists, isoproterenol was most potent, followed in order by epinephrine (Ka = 1.6 x l0-6 M), norepinephrine (Ka = 2.5 x 10-5 M), phenylephrine (Ka > 2.5 x l0-5 M), and dopamine (Ka = 2 x 10-4 M). Isoproterenol activation was blocked by low concentrations of (±)-propranolol (Ki = 2.7 x 10-9 M) but only by higher concentrations of (+)-propranolol (Ki = 3 x 10-6 M), fluphenazine (Ki = 1.2 x 10-7 M), or phentolamine (Ki > l0-3 M). Among the more selective β-adrenergic agents, the relatively β2-selective agonists, zinterol (Ka = 2.3 x 10-8 M) and OPC 2009 (Ka = 1.3 x 10-7 M), were much more potent and effective than the β1-selective agonist, prenalterol. Salbutamol, terbutaline, and orciprenaline were of intermediate potency and, along with zinterol, acted as partial agonists. Among several antagonists (IPS 339, H35/25, butoxamine, metoprolol, p-oxyprenolol, atenolol, and practolol), the calculated inhibitory constants correlated well with those obtained for the same agents in blocking isoproterenol-stimulated adenylate cyclase and IHYP binding in lung. Both agonist and antagonist data indicated that the majority of the adenylate cyclase-associated β receptors in choroid plexus were β2. Anatomical studies indicated that β-adrenergic-sensitive adenylate cyclase activity was greater in fourth ventricle than lateral ventricle choroid plexus. Cell separation experiments, utilizing several different procedures, consistently demonstrated substantial enrichment of hormone sensitivity in fractions enriched in epithelial as compared with vascular elements. The results suggest a possible β2-adrenergic regulation of choroid plexus secretory epithelium.