Pape L, Kristensen B I
Biochim Biophys Acta. 1984 Feb 29;770(1):1-6. doi: 10.1016/0005-2736(84)90065-8.
The role of calmodulin in stimulating active calcium transport in the human red cell membrane is well documented. In contrast, efforts to characterize the effect of calmodulin on the Ca2+-dependent K+ channel in erythrocyte membranes have given rise to conflicting reports. These studies have indicated that experimental conditions may play a critical role in preserving the Ca2+-dependent K+ channels in erythrocyte inside-out vesicles. With these observations in mind, a double-labelling study of simultaneous active Ca2+ and passive Rb+ uptake in red-cell inside-out vesicles was undertaken. Addition of calmodulin and ATP to a suspension of inside-out vesicles containing 1 mM K+ caused a Ca2+-dependent increase in both the rate of active calcium transport and Rb+ uptake. The initial Rb+ isotope flux was increased 3-fold over the rate observed in the absence of calmodulin. The k1/2 for activation of K+ permeability was approx. 5 X 10(-7) M Ca2+ as compared to 10(-6) M Ca2+ for active Ca2+ transport. Addition of the calmodulin antagonists pimozide and chlorpromazine blocked calmodulin activation of the Ca2+-dependent K+ channel. The observation that activation of the K+ channel occurs at Ca2+ concentrations which are lower than those required for maximum stimulation of the calcium pump suggests that these processes are dependent on two states of the calmodulin molecule, characterized by a lower or higher amount of Ca2+ bound to calmodulin.
钙调蛋白在刺激人红细胞膜上的主动钙转运中的作用已有充分记录。相比之下，关于钙调蛋白对红细胞膜中钙依赖性钾通道影响的表征研究却得出了相互矛盾的报告。这些研究表明，实验条件可能在维持红细胞内翻囊泡中的钙依赖性钾通道方面起着关键作用。基于这些观察结果，我们对红细胞内翻囊泡中同时进行的主动钙摄取和被动铷摄取进行了双标记研究。向含有1 mM钾的内翻囊泡悬浮液中添加钙调蛋白和ATP，会导致主动钙转运速率和铷摄取均出现钙依赖性增加。初始铷同位素通量比在无钙调蛋白时观察到的速率增加了3倍。钾通透性激活的k1/2约为5×10^(-7) M Ca2+，而主动钙转运的k1/2为10^(-6) M Ca2+。添加钙调蛋白拮抗剂匹莫齐特和氯丙嗪可阻断钙调蛋白对钙依赖性钾通道的激活。钾通道在低于最大刺激钙泵所需浓度的钙浓度下被激活，这一观察结果表明，这些过程依赖于钙调蛋白分子的两种状态，其特征是与钙调蛋白结合的钙量较低或较高。
