Ozbasli C F, Fadda G Z, Levi E, Massry S G
Department of Medicine, University of Southern California, School of Medicine, Los Angeles 90033.
Miner Electrolyte Metab. 1992;18(6):382-5.
The Vmax of Ca2+ ATPase of pancreatic islets is reduced in states of chronic excess of PTH. This has been attributed to the reduced ATP content of pancreatic islet and to impaired response of the enzyme to calmodulin. It is also possible that excess PTH directly inhibits the activity of islet Ca2+ ATPase. The present study examined this issue. Small doses of 1-84 PTH (0.0625 and 0.125 x 10(-7) M) stimulated while larger doses (0.25, 0.5, 1.0, 2.0 and 4.0 x 10(-7) M) inhibited the activity of Ca2+ ATPase of intact islets. PTH has no effect on Ca2+ ATPase when the hormone was added to preparation of membrane homogenate of islets. Verapamil abolished both the stimulatory as well the inhibitory effects of PTH on Ca2+ ATPase of intact islets. The data indicate that PTH does not have a direct effect on the Vmax of islet Ca2+ ATPase of islet. Its effect on the enzyme activity of intact islet is most likely mediated through the hormone-induced calcium influx.
在慢性甲状旁腺激素（PTH）过量状态下，胰岛Ca2+ATP酶的最大反应速度（Vmax）降低。这归因于胰岛ATP含量减少以及该酶对钙调蛋白的反应受损。也有可能是过量的PTH直接抑制了胰岛Ca2+ATP酶的活性。本研究探讨了这个问题。小剂量的1-84 PTH（0.0625和0.125×10^(-7) M）具有刺激作用，而大剂量（0.25、0.5、1.0、2.0和4.0×10^(-7) M）则抑制完整胰岛Ca2+ATP酶的活性。当将该激素添加到胰岛膜匀浆制剂中时，PTH对Ca2+ATP酶没有影响。维拉帕米消除了PTH对完整胰岛Ca2+ATP酶的刺激和抑制作用。数据表明，PTH对胰岛Ca2+ATP酶的Vmax没有直接影响。其对完整胰岛酶活性的影响很可能是通过激素诱导的钙内流介导的。
