Tsuzuki T, Okabe K, Kajiya H, Habu T
Department of Removable Prosthodontics, Fukuoka Dental College, Japan.
Jpn J Physiol. 2000 Feb;50(1):67-76. doi: 10.2170/jjphysiol.50.67.
Although the importance of mechanical stress on bone metabolism is well known, the intracellular mechanisms involved are not well understood. To evaluate the role of mechanical stress on osteoclastic function, we investigated the effects of membrane stretch induced by osmotic cell swelling on cytosolic Ca(2+) and bone resorption activity in freshly isolated rat osteoclasts. The intracellular Ca(2+) concentration (Ca(2+)) was measured by fura-2 microspectrofluorimetry. Exposure to hypotonic solution (211-151 mOsm) caused cell swelling and reversibly increased Ca(2+) in the osteoclasts. This Ca(2+) increase was abolished by the omission of extracellular Ca(2+), but was not affected by the depletion of intracellular Ca(2+) stores. Gd(3+) and La(3+) inhibited the swelling-induced Ca(2+) increase, while nifedipine and Bay K 8644 did not. Neither protein kinase A inhibitors (Rp-cAMP, H-89) nor protein kinase C inhibitors (staurosporine, chelerythrine) affected the Ca(2+) increase. Membrane depolarization was not essential for the Ca(2+) increase either. To assess the effects of membrane stretch on the bone resorption activity of osteoclasts, we investigated actin ring formation, the intracellular structure responsible for bone resorption in osteoclasts. Hypotonic stimulation acutely disrupted actin ring formation in an extracellular Ca(2+)-dependent manner, and this disruption was prevented by Gd(3+). Moreover, Ca(2+) ionophore (ionomycin) also induced disruption of the actin rings. These results indicate that mechanical stress inhibits osteoclastic bone resorption activity, possibly via the elevation of Ca(2+) through stretch-activated, non-selective cation channels.
尽管机械应力对骨代谢的重要性已广为人知，但其中涉及的细胞内机制仍未完全明晰。为评估机械应力对破骨细胞功能的作用，我们研究了渗透细胞肿胀诱导的膜拉伸对新鲜分离的大鼠破骨细胞胞质Ca(2+)及骨吸收活性的影响。通过fura - 2显微分光荧光测定法测量细胞内Ca(2+)浓度(Ca(2+))。暴露于低渗溶液(211 - 151 mOsm)会导致细胞肿胀，并使破骨细胞内的Ca(2+)可逆性增加。这种Ca(2+)的增加在细胞外Ca(2+)缺失时被消除，但不受细胞内Ca(2+)储存耗尽的影响。Gd(3+)和La(3+)抑制肿胀诱导的Ca(2+)增加，而硝苯地平和Bay K 8644则无此作用。蛋白激酶A抑制剂(Rp - cAMP, H - 89)和蛋白激酶C抑制剂(星形孢菌素, 白屈菜红碱)均不影响Ca(2+)的增加。膜去极化对于Ca(2+)的增加也并非必需。为评估膜拉伸对破骨细胞骨吸收活性的影响，我们研究了肌动蛋白环的形成，这是破骨细胞中负责骨吸收的细胞内结构。低渗刺激以细胞外Ca(2+)依赖的方式急性破坏肌动蛋白环的形成，而Gd(3+)可防止这种破坏。此外，Ca(2+)离子载体(离子霉素)也诱导肌动蛋白环的破坏。这些结果表明，机械应力可能通过拉伸激活的非选择性阳离子通道使Ca(2+)升高，从而抑制破骨细胞的骨吸收活性。
