Tiselius Hans-Göran, Lindbäck Bengt, Fornander Anne-Marie, Nilsson Mari-Anne
Department of Urology, Karolinska University Hospital, Stockholm, Sweden.
Urol Res. 2009 Aug;37(4):181-92. doi: 10.1007/s00240-009-0191-7. Epub 2009 May 15.
Crystals of calcium phosphate (CaP) added to solutions with a composition corresponding to that at different levels of the collecting duct (CD) and with different pH were rapidly dissolved at pH 5.0, 5.25 and 5.5. Only minor or no dissolution was observed at higher pH levels. Despite this effect, CaP crystals induced nucleation or heterogeneous crystallization of CaOx up to a pH of 6.1, whereas CaP was the type of crystalline material that precipitated at higher pH. Accordingly, small crystal volumes were recorded at pH 5.5 and great volumes at pH 6.7 4 h after the addition of CaP crystals to the solutions. Dialyzed urine appeared to counteract the dissolution of CaP and to reduce the rate of secondary crystallization. The CaP induced crystallization of CaOx was confirmed by a reduction of (14)C-labeled oxalate in solution. The AP(CaOx) required for a nucleation or heterogeneous crystallization of CaOx in the presence of CaP was around 1.5 x 10(-8) (mol/l)(2). For CaP crystal formation on CaP, an AP(CaP) ((a)Ca(2+) x (a)PO(4)(3-)) of approximately 50 x 10(-14) (mol/l)(2) appeared to be necessary. The CaOx crystals formed were microscopically found in association with the CaP crystalline material and were most frequently of CaOx dihydrate type. Step-wise crystallization experiments comprising supersaturation with CaP (Step A), supersaturation with CaOx (Step B) and subsequently acidification (Step C) showed that CaOx crystal formation occurred when CaP crystals were dissolved and thereby served as a source of calcium. The ensuing formation of CaOx crystals is most likely the result from high local levels of supersaturation with CaOx caused by the increased concentration of calcium. These experimental studies give support to the hypothesis that crystallization of CaOx at lower nephron levels or in caliceal urine might be induced by dissolution of CaP formed at nephron levels above the CD, and that a low pH is prerequisite for the precipitation of CaOx. The observations accordingly provide additional evidence for the important role of calcium phosphate in the crystallization of calcium oxalate, that might occur both at the surface of Randall's plaques and intratubularly at the papillary tip.
将磷酸钙（CaP）晶体添加到成分与集合管（CD）不同水平以及不同pH值相对应的溶液中，在pH 5.0、5.25和5.5时，CaP晶体迅速溶解。在较高pH值水平下，仅观察到少量溶解或未溶解。尽管有这种影响，但在pH值达到6.1之前，CaP晶体都会诱导草酸钙（CaOx）的成核或异质结晶，而在较高pH值下沉淀的晶体物质类型为CaP。因此，在向溶液中添加CaP晶体4小时后，在pH 5.5时记录到的晶体体积较小，而在pH 6.7时记录到的晶体体积较大。透析后的尿液似乎可以抵消CaP的溶解，并降低二次结晶的速率。溶液中（14）C标记的草酸盐减少证实了CaP诱导的CaOx结晶。在CaP存在的情况下，CaOx成核或异质结晶所需的AP（CaOx）约为1.5×10^(-8) （mol/l）^2。对于CaP晶体在CaP上的形成，AP（CaP）（（a）Ca^(2+)×（a）PO4^(3-)）约为50×10^(-14) （mol/l）^2似乎是必要的。显微镜下发现形成的CaOx晶体与CaP晶体物质相关联，并且最常见的是二水合CaOx类型。包括用CaP过饱和（步骤A）、用CaOx过饱和（步骤B）以及随后酸化（步骤C）的逐步结晶实验表明，当CaP晶体溶解并因此作为钙源时，会发生CaOx晶体形成。随后形成的CaOx晶体很可能是由于钙浓度增加导致局部CaOx过饱和水平升高的结果。这些实验研究支持了以下假设：在肾单位较低水平或肾盏尿液中CaOx的结晶可能是由在CD上方肾单位水平形成的CaP溶解所诱导的，并且低pH值是CaOx沉淀的先决条件。因此，这些观察结果为磷酸钙在草酸钙结晶中的重要作用提供了额外证据，草酸钙结晶可能发生在兰德尔斑的表面以及乳头尖端的肾小管内。
