Sprague S M, Popovtzer M M, Dranitzki-Elhalel M, Wald H
Section of Nephrology and Hypertension, Hadassah University Hospital, Hebrew University, Jerusalem, Israel.
Am J Physiol. 1996 Dec;271(6 Pt 2):F1139-46. doi: 10.1152/ajprenal.1996.271.6.F1139.
Activation of adenylate cyclase is believed to be the major intracellular mediator of bone resorption induced by parathyroid hormone (PTH), prostaglandins, and various bone resorbing cytokines. Studies have demonstrated a dissociation between PTH-induced bone resorption and adenosine 3',5'-cyclic monophosphate (cAMP) formation, as well as suggested a role of protein kinase C (PKC) in mediating in part the actions of PTH. We therefore investigated the relative contribution of the adenylate cyclase or PKC signal transduction pathways in mediating the PTH-induced net calcium release from cultured neonatal calvariae, an in vitro model of bone resorption. PTH (10(-11) to 10(-7) M) caused a dose-dependent increase in calcium efflux from cultured bone and activated both cAMP and PKC. To determine the role of each of these second messengers in mediating PTH-induced calcium release from bone, calvariae were preincubated with either the adenylate cyclase inhibitor SQ-22536 (10(-5) to 10(-4) M) or the PKC inhibitor staurosporine (10(-7) M) before coincubation with PTH. Compared with control, PTH caused a significant calcium efflux, whereas preincubation with SQ-22536 had no effect on basal calcium efflux and partially inhibited the calcium efflux caused by PTH. In contrast preincubation with staurosporine completely obliterated the PTH-induced calcium efflux. PTH is a potent stimulator of calcium release and activates both the cAMP and PKC signal transduction pathways in cultured bone. Inhibition of PTH-stimulated PKC activity completely abolished the PTH-induced calcium efflux from calvariae, whereas PTH-induced calcium efflux persisted despite adenylate cyclase inhibition. Thus the bone resorbing effect of PTH appears to be dependent predominantly on activation of PKC.
腺苷酸环化酶的激活被认为是甲状旁腺激素（PTH）、前列腺素和各种骨吸收细胞因子诱导骨吸收的主要细胞内介质。研究表明，PTH诱导的骨吸收与腺苷3',5'-环磷酸（cAMP）形成之间存在解离，同时也提示蛋白激酶C（PKC）在部分介导PTH的作用中发挥作用。因此，我们研究了腺苷酸环化酶或PKC信号转导途径在介导PTH诱导的培养新生颅骨净钙释放中的相对贡献，这是一种骨吸收的体外模型。PTH（10^(-11)至10^(-7) M）导致培养骨中钙流出呈剂量依赖性增加，并激活了cAMP和PKC。为了确定这些第二信使在介导PTH诱导的骨钙释放中的作用，在与PTH共同孵育之前，将颅骨预先与腺苷酸环化酶抑制剂SQ-22536（10^(-5)至10^(-4) M）或PKC抑制剂星形孢菌素（10^(-7) M）预孵育。与对照组相比，PTH导致显著的钙流出，而与SQ-22536预孵育对基础钙流出没有影响，并部分抑制了PTH引起的钙流出。相反，与星形孢菌素预孵育完全消除了PTH诱导的钙流出。PTH是钙释放的有效刺激剂，并激活培养骨中的cAMP和PKC信号转导途径。抑制PTH刺激的PKC活性完全消除了PTH诱导的颅骨钙流出，而尽管腺苷酸环化酶受到抑制，PTH诱导的钙流出仍然存在。因此，PTH的骨吸收作用似乎主要依赖于PKC的激活。
