Establishment of a Parathyroid Hormone-Responsive Phosphate Transport System in Vitro Using Cultured Renal Cells*

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Abstract
A new system was established using primary cultured mouse kidney epithelial cells to study the effect of PTH on renal tubular phosphate transport. The cells used in our study had alkaline phosphatase activity. They showed increased cAMP content in response to PTH, calcitonin, and vasopressin. Thus, these cells were thought to be a mixture of cells originating from the proximal and distal renal tubules. To explore the mechanism of phosphate handling in these cells, the accumulation of radioactive phosphate from the medium into the cells and the spaces between the cell layer and culture plate (submonolayer spaces) was measured. The accumulation of phosphate by the cells was a sodium-dependent, energy-dependent process, which was demonstrated by inhibition both in the absence of sodium and in the presence of ouabain or 2,4-dinitrophenol. Furthermore, phosphate accumulation was decreased significantly by PTH presumably acting through cAMP. PTH inhibited phosphate accumulation not by affecting the efflux process, but by affecting the uptake process through the apical membrane of the cultured cells without altering the compartmental distribution of the accumulated phosphate. These characteristics of phosphate accumulation resemble those of renal tubular phosphate transport.