Eberhard M, Miyagawa K, Hermsmeyer K, Erne P
Department of Research, Kantonsspital, Basel, Switzerland.
Naunyn Schmiedebergs Arch Pharmacol. 1995 Dec;353(1):94-101. doi: 10.1007/BF00168921.
The Ca2+ antagonist mibefradil at supratherapeutic concentrations induced a sustained increase of cytosolic Ca2+ in cultured rat cardiac fibroblasts and human platelets which lack sensitivity to K+ depolarization and Ca2+ channel block by verapamil or other Ca2+ antagonists. At concentrations above 10 microM, mibefradil elevated substantially cytosolic [Ca2+] without affecting the peak level of agonist-induced Ca2+ transients. These Ca2+-mobilizing actions of 10 or 100 microM mibefradil stand in contrast to the Ca2+ antagonism and relaxation of vascular muscle at 1 microM concentrations. Since a substantial part of mibefradil-induced increase in cytosolic Ca2+ was independent of extracellular Ca2+, and in order to define better the mechanism of Ca2+ increase, we exposed permeabilized cultured rat cardiac fibroblasts and human platelets to mibefradil at concentrations sufficiently high to identify covert effects. In permeabilized fibroblasts or platelets mibefradil at concentrations above 10 microM activated dose-dependent Ca2+ release from intracellular Ca2+ stores. Verapamil had no effect at concentrations of up to 100 microM. Mibefradil-induced Ca2+ release was not affected by ryanodine, thapsigargin, removal of ATP or dithioerythreitol, indicating that neither Ca2+ - nor disulfide reagent-induced Ca2+ release were involved and that mibefradil did not release Ca2+ by inhibition of the Ca2+-ATPase pump of endoplasmic reticulum. The rate, but not the amplitude, of mibefradil-induced Ca2+ release is increased up to fourfold in the presence of pentosan polysulphate or heparin, two potent inhibitors of inositol 1,4,5-trisphosphate-induced Ca2+ release. Depletion of Ca2+ stores of permeabilized cells inositol 1,4,5-trisphosphate in the presence of thapsigargin completely blocked mibefradil-induced Ca2+ release, and depletion of Ca2+ stores by mibefradil prevented further Ca2+ release by inositol 1,4,5-trisphosphate. Mibefradil at supratherapeutic concentrations (> or = microM) thus mobilized Ca2+ from an inositol 1,4,5-trisphosphate-sensitive Ca2+ pool in cultured rat cardiac fibroblasts and human platelets.
超治疗浓度的钙拮抗剂米贝拉地尔可使培养的大鼠心脏成纤维细胞和人血小板中的胞质钙持续增加，这些细胞对钾离子去极化以及维拉帕米或其他钙拮抗剂引起的钙通道阻滞不敏感。在浓度高于10微摩尔时，米贝拉地尔可大幅提高胞质[Ca2+]水平，而不影响激动剂诱导的钙瞬变峰值。10或100微摩尔米贝拉地尔的这些钙动员作用与1微摩尔浓度时的钙拮抗作用及血管平滑肌舒张作用形成对比。由于米贝拉地尔诱导的胞质钙增加的很大一部分与细胞外钙无关，为了更好地确定钙增加的机制，我们将透化的培养大鼠心脏成纤维细胞和人血小板暴露于浓度足够高的米贝拉地尔中，以识别潜在影响。在透化的成纤维细胞或血小板中，浓度高于10微摩尔的米贝拉地尔可激活剂量依赖性的细胞内钙库钙释放。维拉帕米在浓度高达100微摩尔时无作用。米贝拉地尔诱导的钙释放不受ryanodine、毒胡萝卜素、ATP去除或二硫苏糖醇的影响，这表明既不涉及钙诱导的也不涉及二硫试剂诱导的钙释放，且米贝拉地尔不是通过抑制内质网的钙ATP酶泵来释放钙的。在存在戊聚糖多硫酸盐或肝素（两种肌醇1,4,5-三磷酸诱导的钙释放的有效抑制剂）的情况下，米贝拉地尔诱导的钙释放速率增加高达四倍，但幅度不变。在毒胡萝卜素存在的情况下，用肌醇1,4,5-三磷酸耗尽透化细胞的钙库可完全阻断米贝拉地尔诱导的钙释放，而米贝拉地尔耗尽钙库可阻止肌醇1,4,5-三磷酸进一步释放钙。因此，超治疗浓度（≥1微摩尔）的米贝拉地尔可从培养的大鼠心脏成纤维细胞和人血小板中的肌醇1,4,5-三磷酸敏感钙池中动员钙。
