Piascik M T, Babich M, Rush M E
J Biol Chem. 1983 Sep 25;258(18):10913-8.
The Ca2+-dependent regulation of the adenylate cyclase activity associated with microsomes isolated from bovine aortic smooth muscle has been studied. Calmodulin content of microsomal membranes employed in these studies was 80 +/- 14 ng/mg as determined by specific radioimmunoassay. In the absence of exogenous calmodulin, Ca2+ concentrations greater than 0.8 microM inhibited adenylate cyclase activity with one-half-maximal inhibition occurring at 2.5 microM Ca2+. In the presence of 5 or 9 microM bovine testis calmodulin, Ca2+ stimulated smooth muscle adenylate cyclase activity with one-half-maximal stimulation occurring at 0.2 microM for both 5 and 9 microM calmodulin. Calmodulin stimulation was observed between 0.1 and 0.8 microM Ca2+. Despite the presence of calmodulin, Ca2+ concentrations greater than 0.8 microM were inhibitory to smooth muscle adenylate cyclase activity. However, calmodulin reduced the sensitivity of the enzyme to inhibition by Ca2+. Trifluoperazine (100 microM) reversed both the calmodulin-dependent stimulation of cyclase activity and the calmodulin-induced decrease in sensitivity to the inhibitory actions of Ca2+. Trifluoperazine alone shifted the curve describing Ca2+ inhibition of cyclase activity to the left. The value of Ca2+ for one-half-maximal inhibition decreased from 2.9 to 1.2 microM. The trifluoperazine-induced shift was reversed by exogenous calmodulin. These data suggest: 1) Ca2+, at physiological concentrations, can stimulate as well as inhibit smooth muscle adenylate cyclase activity; 2) the stimulation of adenylate cyclase activity is mediated by calmodulin; 3) the Ca2+-calmodulin complex reduces the sensitivity of smooth muscle adenylate cyclase to the inhibitory actions of Ca2+; and 4) the level of calmodulin associated with smooth muscle adenylate cyclase may modulate the response (both stimulatory and inhibitory) of the enzyme to Ca2+.
对从牛主动脉平滑肌分离出的微粒体相关的腺苷酸环化酶活性的钙依赖性调节进行了研究。通过特异性放射免疫测定法确定，这些研究中使用的微粒体膜的钙调蛋白含量为80±14 ng/mg。在没有外源性钙调蛋白的情况下，大于0.8微摩尔/升的钙离子浓度会抑制腺苷酸环化酶活性，在2.5微摩尔/升钙离子时出现半数最大抑制。在存在5或9微摩尔/升牛睾丸钙调蛋白的情况下，钙离子刺激平滑肌腺苷酸环化酶活性，对于5和9微摩尔/升的钙调蛋白，在0.2微摩尔/升时出现半数最大刺激。在0.1至0.8微摩尔/升的钙离子浓度范围内观察到钙调蛋白的刺激作用。尽管存在钙调蛋白，但大于0.8微摩尔/升的钙离子浓度对平滑肌腺苷酸环化酶活性仍有抑制作用。然而，钙调蛋白降低了该酶对钙离子抑制的敏感性。三氟拉嗪（100微摩尔/升）可逆转钙调蛋白依赖性的环化酶活性刺激以及钙调蛋白诱导的对钙离子抑制作用敏感性的降低。单独使用三氟拉嗪会使描述钙离子对环化酶活性抑制的曲线向左移动。半数最大抑制时的钙离子值从2.9微摩尔/升降至1.2微摩尔/升。三氟拉嗪诱导的移位可被外源性钙调蛋白逆转。这些数据表明：1）生理浓度的钙离子既能刺激也能抑制平滑肌腺苷酸环化酶活性；2）腺苷酸环化酶活性的刺激由钙调蛋白介导；3）钙离子-钙调蛋白复合物降低了平滑肌腺苷酸环化酶对钙离子抑制作用的敏感性；4）与平滑肌腺苷酸环化酶相关的钙调蛋白水平可能调节该酶对钙离子的反应（刺激和抑制）。
