Dube M P, Davis F B, Davis P J, Blas S D
Department of Medicine, State University of New York at Buffalo School of Medicine.
Mol Endocrinol. 1987 Feb;1(2):168-71. doi: 10.1210/mend-1-2-168.
Thyroid hormone (10(-11) to 10(-10) M) stimulates plasma membrane Ca2+-ATPase activity in vitro in various tissues, including the human red cell (RBC), by a calmodulin-requiring mechanism. Bepridil and cetiedil are Ca2+ antagonists with an intracellular (calmodulin-antagonist) site of action, as well as an effect on the calcium channel in excitable tissues. We have studied the actions of bepridil and cetiedil on Ca2+-ATPase in a channel-free membrane (RBC) to determine effectiveness of these agents as inhibitors of thyroid hormone action on the enzyme. Dose-response studies showed that thyroid hormone stimulation of Ca2+-ATPase activity in vitro was significantly inhibited by as little as 2 x 10(-5) M bepridil and cetiedil. IC50 values of bepridil and cetiedil for thyroid hormone response of the enzyme were 5 x 10(-5) and 2 x 10(-5) M, respectively, whereas IC50s of these agents for enzyme activity in the absence of thyroid hormone were both 10(-4) M. Progressive addition of purified rat testis calmodulin in vitro (10-150 ng calmodulin/mg membrane protein) restored hormone responsiveness in the presence of bepridil and cetiedil. Binding of labeled thyroid hormone by RBC membranes was unaffected by bepridil and cetiedil (up to 2 x 10(-4) M). Thus, bepridil and cetiedil are Ca2+ antagonists that reversibly inhibit thyroid hormone action on human RBC Ca2+-ATPase by a calmodulin-dependent mechanism. Thyroid hormone effect on Ca2+-ATPase is more susceptible to bepridil and cetiedil inhibition than is basal enzyme activity.
甲状腺激素（10⁻¹¹至10⁻¹⁰M）通过一种需要钙调蛋白的机制，在体外刺激包括人红细胞（RBC）在内的各种组织中的质膜Ca²⁺ - ATP酶活性。苄普地尔和西替地尔是具有细胞内（钙调蛋白拮抗剂）作用位点的Ca²⁺拮抗剂，并且对可兴奋组织中的钙通道有影响。我们研究了苄普地尔和西替地尔在无通道膜（红细胞）中对Ca²⁺ - ATP酶的作用，以确定这些药物作为甲状腺激素对该酶作用的抑制剂的有效性。剂量反应研究表明，体外甲状腺激素对Ca²⁺ - ATP酶活性的刺激作用，低至2×10⁻⁵M的苄普地尔和西替地尔就能显著抑制。苄普地尔和西替地尔对该酶甲状腺激素反应的IC50值分别为5×10⁻⁵和2×10⁻⁵M，而在无甲状腺激素时这些药物对酶活性的IC50均为10⁻⁴M。在体外逐步添加纯化的大鼠睾丸钙调蛋白（10 - 150 ng钙调蛋白/mg膜蛋白）可在苄普地尔和西替地尔存在的情况下恢复激素反应性。红细胞膜对标记甲状腺激素的结合不受苄普地尔和西替地尔（高达2×10⁻⁴M）的影响。因此，苄普地尔和西替地尔是Ca²⁺拮抗剂，它们通过钙调蛋白依赖性机制可逆地抑制甲状腺激素对人红细胞Ca²⁺ - ATP酶的作用。甲状腺激素对Ca²⁺ - ATP酶的作用比基础酶活性更容易受到苄普地尔和西替地尔的抑制。
