Moore E W, Verine H J
Am J Physiol. 1987 May;252(5 Pt 1):G707-18. doi: 10.1152/ajpgi.1987.252.5.G707.
CaCO3 is a major constituent of pancreatic stones, salivary stones, and many pigment gallstones. Elucidation of the physicochemical state of calcium is necessary for definition of calcium solubility in these systems. Pancreatic stones are observed in both humans and cattle, and are approximately 95% CaCO3 (calcite) in both species. Despite its importance, little is known about the physicochemical state of calcium in pancreatic juice. This paper presents an a priori model, based on established physicochemical principles, for the state of calcium in the juice at all levels of secretion. Two postulates of the model are the following: the limiting free [Ca2+] in the juice is governed by the solubility product (K' sp) for CaCO3; if K' sp is exceeded, the juice is supersaturated and precipitation of CaCO3 is thermodynamically possible; total calcium, [Ca], in the juice is the sum of four distinct species: free ionized calcium, Ca2+; calcium-bicarbonate complex, CaHCO3+; calcium carbonate ion-pair, CaCO3(0); and protein-bound calcium, CaProt. Overall equations of the model and graphical corollaries are presented. The model predicts an inverse hyperbolic relationship between [Ca2+] or [Ca] and [HCO3-]. Calcium solubility is maximal at low [HCO3-]; as [HCO3-] increases, both [Ca2+] and [Ca] decline to respective limiting values of approximately 0.015 and 0.15 mM. At low [HCO3-], most of [Ca] is present as Ca2+ and CaProt, whereas at high [HCO3-], most [Ca] is CaHCO3+ and CaCO3(0). Protein, HCO3-, and CO3(2-) ions are thus important buffers for Ca2+ in the juice. The model provides a quantitative framework for further elucidation of calcium lithogenicity in the pancreas, salivary gland, and biliary tract.
碳酸钙是胰石、涎石和许多色素性胆结石的主要成分。阐明钙的物理化学状态对于确定这些系统中钙的溶解度至关重要。在人类和牛中都观察到胰石，并且在这两个物种中胰石大约95%是碳酸钙（方解石）。尽管其很重要，但关于胰液中钙的物理化学状态却知之甚少。本文基于已确立的物理化学原理，提出了一个关于不同分泌水平下胰液中钙状态的先验模型。该模型的两个假设如下：胰液中极限游离[Ca2+]受碳酸钙的溶度积（K'sp）控制；如果超过K'sp，胰液就会过饱和，碳酸钙沉淀在热力学上是可能的；胰液中的总钙[Ca]是四种不同形态钙的总和：游离离子钙Ca2+；碳酸氢钙络合物CaHCO3+；碳酸钙离子对CaCO3(0)；以及与蛋白质结合的钙CaProt。给出了该模型的总体方程和图形推论。该模型预测[Ca2+]或[Ca]与[HCO3-]之间呈反双曲线关系。钙溶解度在低[HCO3-]时最大；随着[HCO3-]增加，[Ca2+]和[Ca]都会下降到各自约0.015和0.15 mM的极限值。在低[HCO3-]时，大部分[Ca]以Ca2+和CaProt形式存在，而在高[HCO3-]时，大部分[Ca]是CaHCO3+和CaCO3(0)。因此，蛋白质、HCO3-和CO3(2-)离子是胰液中Ca2+的重要缓冲剂。该模型为进一步阐明胰腺、唾液腺和胆道中钙的致石性提供了一个定量框架。
