title: Voltage dependence of transepithelial guanidine permeation across Caco-2 epithelia allows determination of the paracellular flux component.
abstract: OBJECTIVE
  The aim of this study was to investigate transepithelial ionic permeation via the paracellular pathway of human Caco-2 epithelial monolayers and its contribution to absorption of the base guanidine.
  
  
  METHODS
  Confluent monolayers of Caco-2 epithelial cells were mounted in Ussing chambers and the transepithelial conductance and electrical potential difference (p.d.) determined after NaCl dilution or medium Na substitution (bi-ionic conditions). Guanidine absorption (Ja-b) was measured +/- transepithelial potential gradients using bi-ionic p.d.'s.
  
  
  RESULTS
  Basal NaCl replacement with mannitol gives a transepithelial dilution p.d. of 28.0 +/- 3.1 mV basal solution electropositive (PCl/PNa = 0.34). Bi-ionic p.d.'s (basal replacements) indicate a cation selectivity of NH4+ > K+ approximately Cs+ > Na+ > Li+ > tetraethylammonium+ > N-methyl-D: -glucamine+ approximately choline+. Transepithelial conductances show good correspondence with bi-ionic potential data. Guanidine Ja-b was markedly sensitive to imposed transepithelial potential difference. The ratio of guanidine to mannitol permeability (measured simultaneously) increased from 3.6 in the absence of an imposed p.d. to 13.8 (basolateral negative p.d.).
  
  
  CONCLUSIONS
  Hydrated monovalent ions preferentially permeate the paracellular pathway (Eisenman sequence 2 or 3). Guanidine may access the paracellular pathway because absorptive flux is sensitive to the transepithelial potential difference. An alternative method to assess paracellular-mediated flux of charged organic molecules is suggested.
authors.affiliation: Institute for Cell and Molecular Biosciences, Medical School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.
authors.forename: Georgina
authors.initials: G
authors.lastname: Carr
authors.forename: Iain S
authors.initials: IS
authors.lastname: Haslam
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Simmons
mesh_terms: D018938:Caco-2 Cells / Q000378:metabolism*; D004553:Electric Conductivity; D019791:Guanidine / Q000378:metabolism*; D006801:Humans; D007408:Intestinal Absorption; D007700:Kinetics; D008353:Mannitol / Q000378:metabolism; D008564:Membrane Potentials; D010539:Permeability; D012964:Sodium / Q000378:metabolism
chemical_list: D008353:Mannitol; D012964:Sodium; D019791:Guanidine