Argentino L, Colucci S, Grano M, Barattolo R, Zambonin Zallone A, Teti A
Istituto di Anatomia Umana Normale, Università di Bari.
Boll Soc Ital Biol Sper. 1992 Apr;68(4):245-8.
Osteoclasts display a membrane Ca(2+)-sensing mechanism capable of detecting the extracellular calcium concentration ([Ca2+]o), and to induce increase of [Ca2+]i and inhibition of bone resorption. The ultimate result of the stimulation of such sensing is probably the activation of protein kinase C (PKC). To demonstrate whether PKC plays a role in the control of the osteoclast activity, we treated rabbit single osteoclasts with agents known to activate or to inhibit the enzyme. We measured [Ca2+]i in single fura 2-loaded single cells and found that activation of PKC by phorbol esters doubled the [Ca2+]o-induced [Ca2+]i elevation, whereas inhibition of the enzyme by H7, staurosporine or sphingosine, completely blocked the ability of the cell to respond to elevated [Ca2+]i. By contrast, a control inactive agent, 4Aphorbol, failed to modify the cellular response to elevated [Ca2+]o. We conclude that PKC plays a synergistic role in the regulation of osteoclast Ca(2+)-sensing. Since we have previously demonstrated that activation of PKA up-regulates the Ca(2+)-sensing as well, we hypothesize that such mechanism is positively fed-back by both PKA and PKC-dependent threonine/serine phosphorylations.
破骨细胞表现出一种膜钙（Ca2+）传感机制，能够检测细胞外钙浓度（[Ca2+]o），并诱导细胞内钙浓度（[Ca2+]i）升高和抑制骨吸收。这种传感刺激的最终结果可能是蛋白激酶C（PKC）的激活。为了证明PKC是否在破骨细胞活性控制中发挥作用，我们用已知能激活或抑制该酶的试剂处理兔单个破骨细胞。我们在单个负载fura 2的单细胞中测量了[Ca2+]i，发现佛波酯激活PKC使[Ca2+]o诱导的[Ca2+]i升高加倍，而H7、星形孢菌素或鞘氨醇抑制该酶则完全阻断了细胞对升高的[Ca2+]o作出反应的能力。相比之下，对照无活性试剂4-佛波醇未能改变细胞对升高的[Ca2+]o的反应。我们得出结论，PKC在破骨细胞钙（Ca2+）传感调节中起协同作用。由于我们之前已经证明蛋白激酶A（PKA）的激活也会上调钙（Ca2+）传感，我们推测这种机制受到PKA和PKC依赖性苏氨酸/丝氨酸磷酸化的正向反馈。
