Polarized distribution of oxalate transport systems in LLC-PK1 cells, a line of renal epithelial cells

Abstract

Although oxalate is a major component of kidney stones, the factors affecting renal oxalate handling are poorly understood. This uncertainty stems in part from complexities inherent to available preparations; thus the present studies examined oxalate handling in a simpler model system, LLC-PK1 cells, an epithelial cell line of porcine origin. Initial studies on monolayers in dishes demonstrated that these cells accumulate oxalate via a process or processes sensitive to the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Subsequent studies using LLC-PK1 monolayers on membrane filters examined the characteristics and distribution of these transporter(s). At the apical surface, DIDS-sensitive uptake was sensitive to [Cl-] but not [SO4(2-)] or [HCO3-] and was unaffected by alterations in pH or membrane potential. At the basolateral surface, oxalate uptake was [Cl-] insensitive but markedly affected by variation in pH, [SO4(2-)], or [HCO3-]. Uptake at the two membrane surfaces was also differentially affected by transport inhibitors and organic acids. Thus LLC-PK1 cells appear to express unique transporters at each membrane surface: oxalate/Cl- exchange at the apical surface and oxalate/SO4(2-) (or HCO3-) exchange at the basolateral surface.