Kinetic analysis of tetraethylammonium transport in the kidney epithelial cell line, LLC-PK₁

Purpose. The aims of this study were to establish a kinetic means of analyzing the membrane transport of organic cations in renal epithelial cells, and to simultaneously evaluate drug interactions in apical and basolateral membranes. Methods. Tetraethylammonium (TEA) transport was measured using LLC-PK₁ cell monolayers grown on microporous membrane filters. After incubating the cells with unlabeled TEA or other drugs, apical or basolateral medium was changed to that containing labeled TEA, and transcellular transport and cellular accumulation were measured. Clearance from apical medium to cells (CL₁₂), cells to apical medium (CL₂₁), cells to basolateral medium (CL₂₃) and basolateral medium to cells (CL₃₂) were calculated based on a three compartment model. Results. TEA was accumulated progressively in the monolayers from the basolateral side and was transported unidirectionally to the apical side. CL₃₂ was greater than CL₁₂ and CL₂₃ was greater than CL₂₁. Therefore, the rate limiting step of TEA transport from the basolateral to the apical medium was the cell-to-apical step. Go-incubation of TEA with procainamide decreased the transport parameters of TEA, CL₁₂, CL₂₁ and CL₃₂, whereas that with levofloxacin decreased only CL₁₂ and CL₂₁, not affecting the parameters in basolateral membranes. Conclusions. Using a simple model, we analyzed the transport of organic cation in kidney epithelial cell line, LLC-PK₁. This method can be useful for the analysis of cation transport and drug interactions in the apical and basolateral membranes of renal tubules.