LLC-PK1 cells as a model system to study proximal tubule transport of water and other compounds relevant for renal stone disease

LLC-PK1 cells were cultured on a permeable support in a two-compartment cul ture system. Confluent monolayers received an ultrafiltrate-like solution a t the apical side and a plasma-like solution at the basolateral side. The d istribution of various solutes, including phosphate, calcium, and oxalate o ver both compartments was measured in time. The transport of water was moni tored by alterations in fluid concentrations of radiolabeled inulin. Bicarb onate, glucose, and phosphate were transported rapidly from the apical to b asolateral side of the monolayer. Sodium and chloride were reabsorbed witho ut major consequences for the osmolality in the apical and basal fluid. Cal cium and potassium were also reabsorbed, but to a smaller extent than sodiu m. The luminal concentration of oxalate gradually increased to values that were at least three times higher (12.0 +/- 0.4 mu mol/l) than those in the contraluminal fluid (3.8 +/- 0.1 mu mol/l). However, since the luminal rise of oxalate completely matched the rise of inulin in the apical fluid this appeared to be the passive consequence of active water reabsorption rather than of net directed oxalate transport. The LLC-PK1 model could prove usefu l to study the regulation of proximal tubule water transport and its effect on luminal stone salt concentrations under different physiological conditi ons.