Abstract
Transport of phosphate has been studied in subconfluent monolayers of LLC-PK 1 cells. It was found that this transport system shows similar characteristics to those observed in the kidney. Uptake of phosphate is mediated by a Na +-dependent, substrate-saturable process with an apparent K m value for phosphate of 96 ± 15 μmol/1. Kinetic analysis of the effect of Na + indicated that at (pH 7.4) two sodium ions are cotransported with one HPO 4 2− ion (Hill coefficient 1.5) with an apparent K m value for sodium of 56 mmol/l. P i uptake is inhibited by metabolic inhibitors (ouabain and FCCP). In the pH range of 6.6 of 7.4 P i uptake rate does not change significantly, indicating that both the monovalent and the divalent form of phosphate are accepted by the transport system. It is suggested that phosphate is transported by LLC-PK i cells together with sodium (2 Na + :1 HPO 4 2−) in an electroneutral manner down a favourable sodium gradient.
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