Fujimori A, Miyauchi A, Hruska K A, Martin K J, Avioli L V, Civitelli R
Division of Bone and Mineral Diseases, Jewish Hospital of St. Louis, Washington University Medical Center, St. Louis, Missouri.
Am J Physiol. 1993 Jun;264(6 Pt 1):E918-24. doi: 10.1152/ajpendo.1993.264.6.E918.
We have studied the desensitization of the calcium message system to parathyroid hormone (PTH) by monitoring intracellular calcium concentration ([Ca2+]i) in an opossum kidney cell line (OKP). PTH (10(-7) M) caused a transient increase in [Ca2+]i, with an average peak height of 48.7 +/- 4.7% above baseline (n = 32). Cells stimulated with either 10(-7) or 10(-8) M PTH did not respond to a second challenge with a maximal dose (10(-7) M) of the hormone, whereas lower concentrations of PTH (10(-9) M and 10(-10) M) only partially desensitized the cells, since a [Ca2+]i transient of smaller amplitude (12.7 +/- 2.1 and 40.6 +/- 6.2% above baseline, respectively) was observed with a second stimulation. Desensitization developed within 5 min of initial hormone exposure, when PTH receptor binding was not significantly decreased. Maximal reduction of PTH binding sites (37.0 +/- 1.4%) was achieved only after 2 h. Partial desensitization was reproduced by 10(-9) M phorbol 12-myristate 13-acetate (PMA) but not by dibutyryladenosine 3',5'-cyclic monophosphate, and it was blocked by staurosporine. However, staurosporine had no effect on the complete desensitization induced by high doses of PTH. At 10(-9) M, PTH also caused a time-dependent desensitization of the adenosine 3',5'-cyclic monophosphate (cAMP) response, with maximal inhibition achieved after 2 h. PMA also decreased the cAMP response to PTH, but its inhibitory effect was less potent than that of 10(-9) M PTH. Therefore PTH induces a dose-dependent homologous desensitization of the Ca2+ message system in OKP cells, independent of receptor occupancy.(ABSTRACT TRUNCATED AT 250 WORDS)
我们通过监测负鼠肾细胞系（OKP）中的细胞内钙浓度（[Ca2+]i），研究了钙信号系统对甲状旁腺激素（PTH）的脱敏作用。PTH（10^(-7) M）引起[Ca2+]i短暂升高，平均峰值比基线高48.7±4.7%（n = 32）。用10^(-7) M或10^(-8) M PTH刺激的细胞，对该激素最大剂量（10^(-7) M）的第二次刺激无反应，而较低浓度的PTH（10^(-9) M和10^(-10) M）仅使细胞部分脱敏，因为第二次刺激时观察到幅度较小的[Ca2+]i短暂变化（分别比基线高12.7±2.1%和40.6±6.2%）。在最初激素暴露5分钟内就出现了脱敏，此时PTH受体结合未显著减少。仅在2小时后PTH结合位点才达到最大减少（37.0±1.4%）。10^(-9) M佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）可重现部分脱敏，但二丁酰腺苷3',5'-环磷酸（cAMP）不能，且它被星形孢菌素阻断。然而，星形孢菌素对高剂量PTH诱导的完全脱敏无作用。在10^(-9) M时，PTH还引起了cAMP反应的时间依赖性脱敏，2小时后达到最大抑制。PMA也降低了对PTH的cAMP反应，但其抑制作用不如10^(-9) M PTH强。因此，PTH在OKP细胞中诱导Ca2+信号系统的剂量依赖性同源脱敏，与受体占据无关。（摘要截断于250字）
