Summary
Calcifications occurring in arteriosclerotic plaque and other pathological deposits are important health concerns, and the nature of these deposits and their mechanisms of formation warrant investigation. Crystals of the relevant calcium phosphates were equilibrated with the undiluted ultrafiltered human serum (u.f.s.) at 37°C by constant stirring and periodically removing samples for calcium and phosphate analysis and for pH measurement. The solubility measurements were carried out both with and without a 5.5% CO2 atmosphere, the physiological partial pressure of CO2. The apparent ion activity products of well-crystallized dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (OHAp) equilibrated, in u.f.s. were calculated from the calcium and phosphate concentrations and pH in each case for comparison with their known, solubility products. In this way the well-crystallized calcium phosphates serve as fiducial solubility standards, thereby minimizing errors due to complexing of calcium and phosphate ions by u.f.s. constituents. Under 5.5%, CO2 native u.f.s. was found to be substantially undersaturated with respect to DCPD, slightly supersaturated with respect to OCP, and highly supersaturated with respect to OHAp. The ion activity product of DCPD in DCPD-saturated u.f.s. was 2.4×10−7, and the ion activity product of OCP in OCP-saturated u.f.s. was 4×10−49, slightly above their solubility products (Ksp(DCPD)=2.3×10−7, Ksp(OCP)=2.5×10−49). The ion activity products of DCPD and OCP in u.f.s. under CO2 indicate that the concentrations of calcium and phosphate complexing agents (except bicarbonate) are quite low. The u.f.s. remained supersaturated with respect to OHAp even after 2 months of equilibration. This is attributed to the presence of crystal growth inhibitors in u.f.s.
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References
Marshall RW (1976) Plasma fractions. In: Nordin BEC (ed) Calcium phosphate and magnesium metabolism. Churchill Livingstone, Edinburgh, p 162
Moore EW (1970) Ionized calcium in normal serum, ultrafiltrates, and whole blood determined by ion-exchange electrodes. J Clin Invest 49:318–335
Meyer JL, Fleisch H (1984) Determination of calcium phosphate inhibitor activity. Mineral Electrolyte Metab 10:249–258
Rüffenacht HS, Fleisch H (1984) Measurement of inhibitors of calcium phosphate precipitate in plasma ultrafiltrate. Am J Physiol 246 (Renal Fluid Electrolyte Physiol 15):F648-F655
Moreno EC, Brown WE, Osborn G (1960) Solubility of dicalcium phosphate dihydrate in aqueous systems. Soil Science Soc Am Proc 24:94–98
Chickerur NS, Tung MS, Brown WE (1980) A mechanism for incorporation of carbonate into apatite. Calcif Tissue Int 32:55–62
Avnimelech Y, Moreno EC, Brown WE (1973) Solubility and surface properties of finely divided hydroxyapatite. J Res Natl Bur Stand 77A:149–155
Hay DI, Schluckebier SK, Moreno EC (1982) Equilibrium dialysis and ultrafiltration studies of calcium and phosphate binding by human salivary proteins. Implications for salivary supersaturation with respect to calcium phosphate salts. Calcif Tissue Int 34:531–538
Vogel GL, Chow LC, Brown WE (1983) A microanalytical procedure for the determination of calcium, phosphate and fluoride in enamel biopsy samples. Caries Res 17:23–31
Willis JB (1960) The determinations of metals in blood serum by atomic absorption spectroscopy. I. Calcium. Spectrochim Acta 16:259–272
Murphy J, Riley JP (1962) A modified single solution method for the determination of phosphate in natural waters. Anal Chim Acta 27:31–36
McDowell H, Gregory TM, Brown WE (1977) Solubility of Ca5(PO4)3OH in the system Ca(OH)2−H3PO4−H2O at 5, 15, 25 and 37°C. J Res Natl Bur Stand 81A:273–281
Plummer LN, Busenberg E (1982) The solubilities of calcite, aragonite and vaterite in CO2−H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3−CO2−H2O. Geochimica et Cosmochimica Acta 46: 1011–1040
Brown WE (1973) The solubilities of phosphates and other sparingly soluble compounds. In: Griffith J, Beeton A, Spencer JM, Mitchell DT (eds) Environmental phosphorus handbook, John Wiley, New York, p 203
Gron P (1973) The state of calcium and inorganic orthophosphate in human saliva. Archs Oral Biol 18:1365–1378
Lagerlof F (1983) Effects of flow rate and pH on calcium phosphate saturation in human parotid saliva. Caries Res 17:403–411
Siggaard-Andersen O, Thode J, Wandrup J (1981) The concentration of free calcium ions in the blood plasma. Ionized Calcium. Proc 5th Meet Expert Panel on pH and Blood Bases Workshop held in Copenhagen, pp 163–190
Markowitz M, Rotkin L, Rosen JF (1981) Circadian rhythms of blood minerals in humans. Science 213:672–674
Meyer JL, Fleisch H (1984) Calcification inhibitors in rat and human serum and plasma. Biochem Biophys Acta 799:115–121
Thode J, Wandrup F, Siggaard-Andersen O (1982) Evaluation of a new semiautomatic electrode system for simultaneous measurement of ionized calcium and pH. Scand J Clin Lab Invest 42:407–415
Gregory TM, Moreno EC, Brown WE (1970) Solubility of CaHPO4·2H2O in the system Ca(OH)2−H3PO4−H2O at 5, 15, 25 and 37.5°C. J Res Natl Bur Stand 74A:461–475
Madsen HEL (1970) Ionic concentration in calcium phosphate solutions. I. Solutions saturated with respect to brushite or tetracalcium monohydrogen phosphate at 37°C. Acta Chem Scand 24:1671–1676
Shyu LJ, Perrez L, Zawacky SJ, heughebaert JC, Nancollas GH (1982) The solubility of octacalcium phosphate at 37°C in the system Ca(OH)2−H3PO4−KNO3−H2O. J Dent Res 62: 398–400
Brown WE, Chow LC (1983) Surface equilibria of sparingly soluble crystals. Coll and Sur 7:67–80
Larsen MJ, Thorsen A (1984) A comparison of, some effects of fluoride on apatite formation in vitro and in vivo. Calcif Tissue Int 36:690–696
Moreno EC, Zahradnik J (1974) Chemistry of enamel subsurface demineralization in vitro. J Dent Res 53:226–235
Patel PR, Brown WE (1975) Thermodynamic solubility product of human tooth enamel: powdered sample. J Dent Res 54:728–736
Moreno EC, Gregory TM, Brown WE (1968) Preparation and solubility of hydroxyapatite. J Res Natl Bur Stand 72A:773–782
Chuong R (1973) Experimental study of surface and lattice effects on the solubility of hydroxyapatite. J Dent Res 52:911–914
Brown WE, Lehr JR, Smith JP, Frazier AW (1957) Crystallography of octacalcium phosphate. J Am Chem Soc 79:5318
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Eidelman, N., Chow, L.C. & Brown, W.E. Calcium phosphate saturation levels in ultrafiltered serum. Calcif Tissue Int 40, 71–78 (1987). https://doi.org/10.1007/BF02555708
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DOI: https://doi.org/10.1007/BF02555708