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Phosphate transport in immortalized cell cultures from the renal proximal tubule of normal and Hyp Mice: Evidence That the HYP gene locus product is an extrarenal factor
Author(s) -
Nesbitt Teresa,
Econs Michael J.,
Byun Jong K.,
Martel Josée,
Tenenhouse Harriet S.,
Drezner Marc K.
Publication year - 1995
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650100909
Subject(s) - endocrinology , medicine , hypophosphatemia , cotransporter , tubule , kidney , alkaline phosphatase , biology , immortalised cell line , chemistry , cell , biochemistry , enzyme , sodium , organic chemistry
Whether renal phosphate wasting in X‐linked hypophosphatemia (XLH) results from an intrinsic renal or humoral defect remains controversial. In studies of the murine homolog of XLH, harboring the Simian Virus 40 (SV40) large T antigen, we obviated the influence of renal cell heterogeneity and impressed memory by comparing Na + ‐phosphate cotransport in immortalized cells from the S 1 segment of the proximal tubule. Cells from SV40 transgenic normal and Hyp mice exhibit characteristics of differentiated proximal tubule cells including gluconeogenesis and alkaline phosphatase activity. Surprisingly, however, we found two distinct populations of cells from the S 1 proximal tubule of both normal and Hyp mice. In one, PTH treatment increases cAMP accumulation, while in the other both PTH and thyrocalcitonin enhance cAMP production. Kinetic parameters for Na + ‐phosphate cotransport were similar in both subpopulations of cells from normal (K m , 0.29 ± 0.03 vs. 0.39 ± 0.04 mM; V max , 4.6 ± 0.6 vs. 5.2 ± 0.4 nmol/mg/5 minutes) and Hyp mice (0.33 ± 0.02 vs. 0.26 ± 0.04; 6.0 ± 0.7, 4.8 ± 0.6). More importantly, phosphate transport in S 1 cells of either subpopulation from Hyp mice is no different than that of normals. These data indicate that renal proximal tubule cells from Hyp mice have intrinsically normal phosphate transport and support the hypothesis that a humoral abnormality underlies renal phosphate wasting in XLH.