Fluctuations in surface pH of maturing rat incisor enamel are a result of cycles of H+-secretion by ameloblasts and variations in enamel buffer characteristics
Fluctuations in surface pH of maturing rat incisor enamel are a result of cycles of H+-secretion by ameloblasts and variations in enamel buffer characteristics
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DOI：
10.1016/j.bone.2013.12.018
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发表时间：
2014-03-01
期刊：
影响因子：
4.1
通讯作者：
Frische, Sebastian
中科院分区：
文献类型：
--
作者：
Damkier, Helle H.;Josephsen, Kaj;Frische, Sebastian
它是有争议的，如果成釉细胞在成釉器官的成熟区主要缓冲羟基磷灰石（HA）晶体生长释放的质子，或者如果他们定期分泌质子，创造交替的酸性和碱性条件。后一种假设预测交替pH制度在成熟的釉质，这将受到药物干扰成釉细胞H+分泌。本研究采用比色pH指示剂法和比率荧光法测定大鼠切牙成熟区釉质表面pH值。交替的酸性区（pH值降至624 +/- 0.06）和碱性区（pH值高达7.34 +/- 0.08）被发现沿着牙齿与成釉细胞形态周期相一致。在循环模式的基础上，可以看到pH值朝着切缘逐渐降低。长春碱或H ~+-ATP酶抑制剂FR 167356干扰成釉细胞的酸分泌，尤其是在酸性带的早期，釉质表面pH反映了表面PO 43 ~-离子的滴定状态。在观察到的pH值下，PO 43-将被质子化（pKa > 12），HA溶解。然而，通过分子动力学模拟，我们估计在理想HA表面的HP 0（4）（2-）的pKa为4.3。因此，在釉质表面测量的酸性pH值可能仅溶解HA晶体的非完美域，其中PO 43-被较少地静电屏蔽。在重复的碱性/酸性循环，接近完美的HA-域，因此可能会逐渐取代不太完美的HA-域，导致接近完美的HA-crystals.In结论，周期性变化成釉细胞H+-分泌和釉质成熟的程度决定釉质表面pH值。这是根据一个假设，暗示H+-ATP酶介导的酸分泌成釉细胞。(C)2013 Elsevier Inc. All rights reserved.
It is disputed if ameloblasts in the maturation zone of the enamel organ mainly buffer protons released by hydroxyapatite (HA) crystal growth or if they periodically secrete protons to create alternating acidic and alkaline conditions. The latter hypothesis predicts alternating pH regimes in maturing enamel, which would be affected by pharmacological interference with ameloblast H+-secretion. This study tests these predictions.Colorimetric pH-indicators and ratiometric fluorometry were used to measure surface pH in maturation zone enamel of rat incisors. Alternating acidic (down to pH 624 +/- 0.06) and alkaline zones (up to pH 7.34 +/- 0.08) were found along the tooth coinciding with ameloblast morphological cycles. Underlying the cyclic pattern, a gradual decrease in pH towards the incisal edge was seen. Vinblastine or FR167356 (H+-ATPase-inhibitor) disturbed ameloblast acid-secretion, especially in the early parts of acidic zones.Enamel surface pH reflects the titration state of surface PO43--ions. At the pH-values observed, PO43- would be protonated (pKa > 12) and HA dissolved. However, by molecular dynamics simulations we estimate the pKa of HP0(4)(2-) at an ideal HA surface to be 4.3. The acidic pH measured at the enamel surface may thus only dissolve non-perfect domains of HA crystals in which PO43- is less electrostatically shielded. During repeated alkaline/ acidic cycles, near-perfect HA-domains may therefore gradually replace less perfect HA-domains resulting in near-perfect HA-crystals.In conclusion, cyclic changes in ameloblast H+-secretion and the degree of enamel maturation determine enamel surface pH. This is in accordance with a hypothesis implicating H+-ATPase mediated acid-secretion by ameloblasts. (C) 2013 Elsevier Inc. All rights reserved.