The risk of crystallization in solutions, with a composition corresponding to that of urine in various parts of the nephron, was assessed by studying urine samples containing standardized increments of calcium and oxalate concentrations. The experiments were carried out in salt solutions with and without dialysed urine and the appearance of crystals was detected and measured with a Coulter counter. With increased concentrations of calcium, crystals of calcium phosphate were predominantly formed in solutions with a composition corresponding to that in the proximal and distal tubuli, whereas, calcium oxalate was the primary crystallization product in solutions with a composition corresponding to the collecting duct. These conclusions were based on calculations of ion-activity products of calcium oxalate, hydroxyapatite, and calcium hydrogen phosphate, at the first appearance of crystals; studies on crystal morphology with scanning electron microscopy, and precipitation of [14C]-oxalate following addition of calcium. The ion-activity products of calcium oxalate at the first appearance of crystals following addition of oxalate to solutions with a composition corresponding to the collecting duct were significantly lower in the presence of dialysed urine. This might reflect a promoting effect of some macromolecules on the nucleation of calcium oxalate. Dialysed urine in these samples also had a pronounced influence on the development of the crystals by markedly reducing the mean crystal volume during the first hour following the formation of 100 crystals with a diameter between 3.5 and 5 μm. Such an effect was not observed in those solutions in which calcium phosphate crystals had formed.
Lupták, Ján; Bek-Jensen, Hanne; Fornander, Anne-Marie; Höjgaard, Inge; Nilsson, Mari-Anne; and Tiselius, Hans-Göran
"Crystallization of Calcium Oxalate and Calcium Phosphate at Supersaturation Levels Corresponding to Those in Different Parts of the Nephron,"
Scanning Microscopy: Vol. 8
, Article 5.
Available at: https://digitalcommons.usu.edu/microscopy/vol8/iss1/5