Shoback D M, Chen T H, Lattyak B, King K, Johnson R M
Endocrine Research Unit, Veterans Affairs Medical Center, San Francisco, California.
J Bone Miner Res. 1993 Jul;8(7):891-8. doi: 10.1002/jbmr.5650080715.
The addition of Ca2+ or a variety of divalent cations increases intracellular Ca2+ in parathyroid cells and suppresses secretion. Since 1,4,5-inositol trisphosphate (IP3) and 1,3,4,5-inositol tetrakisphosphate (IP4) mediate Ca2+ mobilization in other systems, we examined high Ca(2+)- and Sr(2+)-induced accumulation of IP3 and IP4 isomers by anion-exchange HPLC and measured 1,4,5-IP3 mass in parathyroid cells. Raising extracellular [Ca2+] from 0.5 to 3.0 mM increased 3H-1,4,5-IP3 within 5 s, which was confirmed by mass measurements. 3H-1,3,4-IP3 rose gradually by 10 s and increased for 60 s after the addition of Ca2+. Although we detected no change in 3H-1,3,4,5-IP4, the increase in 3H-1,3,4-IP3 suggests that 3H-1,3,4,5-IP4 was being formed. The addition of 4 mM SrCl2 produced similar changes in 1,4,5-IP3, which were confirmed by mass assay. 3H-1,3,4,5-IP4 did not change. However, Sr2+ induced a gradual increase in 3H-1,3,4-IP3, which remained above control levels for 5 minutes. Isotopic labeling studies in this system may underestimate changes in 1,4,5-IP3 mass, but both mass and radioisotopic analyses indicate that high extracellular Ca2+ and Sr2+ stimulate substantial increases in 1,4,5-IP3 without significant accumulation of 1,3,4,5-IP4. These studies suggest a role for 1,4,5-IP3 in intracellular Ca2+ mobilization by divalent cations in parathyroid cells.
添加Ca2+或多种二价阳离子会增加甲状旁腺细胞内的Ca2+并抑制分泌。由于1,4,5-肌醇三磷酸（IP3）和1,3,4,5-肌醇四磷酸（IP4）在其他系统中介导Ca2+动员，我们通过阴离子交换高效液相色谱法检测了高Ca(2+)和Sr(2+)诱导的IP3和IP4异构体的积累，并测量了甲状旁腺细胞中1,4,5-IP3的质量。将细胞外[Ca2+]从0.5 mM提高到3.0 mM会在5秒内增加3H-1,4,5-IP3，这通过质量测量得到证实。添加Ca2+后，3H-1,3,4-IP3在10秒时逐渐上升，并在60秒内持续增加。尽管我们未检测到3H-1,3,4,5-IP4有变化，但3H-1,3,4-IP3的增加表明正在形成3H-1,3,4,5-IP4。添加4 mM SrCl2会使1,4,5-IP3产生类似变化，这通过质量分析得到证实。3H-1,3,4,5-IP4没有变化。然而，Sr2+会使3H-1,3,4-IP3逐渐增加，并在5分钟内保持高于对照水平。该系统中的同位素标记研究可能低估了1,4,5-IP3质量的变化，但质量和放射性同位素分析均表明，高细胞外Ca2+和Sr2+会刺激1,4,5-IP3大幅增加，而1,3,4,5-IP4没有显著积累。这些研究表明1,4,5-IP3在甲状旁腺细胞中由二价阳离子介导的细胞内Ca2+动员中发挥作用。
