title: Ochratoxin A secretion in primary cultures of rabbit renal proximal tubule cells.
abstract: Primary cultures of rabbit renal proximal tubule cells grown under improved culture conditions were used to study the transepithelial transport of the nephrotoxic mycotoxin ochratoxin A. The basal-to-apical transepithelial flux, i.e., secretion, of this fluorescence organic acid was measured in primary cultures of rabbit renal proximal tubule cells. The basal-to-apical flux of ochratoxin A increased with time and reached a steady state after 12 h. On the other hand, the apical-to-basal flux, i.e., reabsorption, of ochratoxin A was minimal over time. The secretory flux of ochratoxin A was as much as eightfold greater than the reabsorptive flux, indicating that net secretion is the primary mechanism for ochratoxin A clearance by the proximal tubule. The kinetic analysis of ochratoxin A flux revealed secretion to be a saturable and very high-affinity process with an apparent K50 of 0.33 +/- 0.21 mM. A saturating concentration of the prototypical organic anion substrate para-aminohippurate (PAH) reduced ochratoxin A secretion by approximately 75%. The kinetic analysis of PAH inhibition of ochratoxin A secretion revealed an IC50 of 195 mM, which is similar to the IC50 for PAH inhibition of peritubular ochratoxin A uptake in tubule suspensions and the Km, values for peritubular PAH uptake. The organic anions probenecid, octanoate, and alpha-ketoglutarate reduced ochratoxin A excretion to the same degree as PAH, whereas the amino acid phenylalanine had a minimal effect on ochratoxin A secretion. Thus, collectively, these observations indicate that the secretion of ochratoxin A in primary cultures of rabbit renal proximal tubules is limited to the organic anion secretory pathway. The high affinity measured for the basal-to-apical flux of ochratoxin A suggests that at concentrations typical of naturally occurring exposures, transepithelial secretion by the organic anion transport pathway represents a significant avenue for excretion of this mycotoxin by the renal proximal tubule.
authors.affiliation: Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32611-0885, USA. grovesce@mail.vetmed.ufl.edu
authors.forename: C E
authors.initials: CE
authors.lastname: Groves
authors.forename: G
authors.initials: G
authors.lastname: Nowak
authors.forename: M
authors.initials: M
authors.lastname: Morales
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D005260:Female; D019793:Fluorescein; D007444:Inulin; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009793:Ochratoxins / Q000378:metabolism*; D010101:Oxygen Consumption; D011817:Rabbits; D010130:p-Aminohippuric Acid / Q000494:pharmacology
chemical_list: D027321:Anion Transport Proteins; D002352:Carrier Proteins; D009793:Ochratoxins; C025589:ochratoxin A; D007444:Inulin; D019793:Fluorescein; D010130:p-Aminohippuric Acid