title: Role of calcium in the aggregation of particles coated by urinary macromolecules.
abstract: OBJECTIVE
  In urine, aggregation (AGN) of crystal occurs although they are coated by negatively charged urinary macromolecules (UM) and isolated at a distance from each other, where attraction forces become extremely weak. Calcium (Ca) bridges or viscous binding by UM could explain this AGN.
  
  
  METHODS
  Suspensions of Ca oxalate monohydrate (COM) and carboxylated latex (CL) were prepared in buffered water and UM solutions which were obtained from the urine of 6 healthy men. Surface potential or zetapotential (ZP) of the particles was measured at various concentrations of Ca and UM. AGN of CL was monitored determining particle size and optical density.
  
  
  RESULTS
  The ZP of COM was neutralized by Ca and stabilized around -15 mV by UM. In CL, a stable ZP of about -20 mV was achieved at >3 mM Ca. However, to induce AGN further addition of Ca was necessary. AGN then increased independently of ZP with increasing Ca and decreased with increasing UM concentration.
  
  
  CONCLUSIONS
  In CL, two different Ca effects could be distinguished, one on ZP and another on AGN. The latter is probably based on the formation of Ca bridges between particles and is inhibited by a steric barrier of adsorbed UM. A similar mechanism is postulated for crystal aggregation.
authors.affiliation: Stone Research Center Viollier, Biel, Switzerland. johannes.denise.baumann@bluewin.ch
authors.forename: J M
authors.initials: JM
authors.lastname: Baumann
authors.forename: B
authors.initials: B
authors.lastname: Affolter
authors.forename: U
authors.initials: U
authors.lastname: Caprez
authors.forename: C
authors.initials: C
authors.lastname: Clivaz
authors.forename: U
authors.initials: U
authors.lastname: von Arx
mesh_terms: D001669:Biochemical Phenomena; D002118:Calcium / Q000737:chemistry*; D003460:Crystallization; D006801:Humans; D046911:Macromolecular Substances / Q000737:chemistry* / Q000652:urine*; D008297:Male
chemical_list: D046911:Macromolecular Substances; D002118:Calcium