Calcitriol stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism.

Academic Article

Abstract

  • Calcitriol (CT) stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism. An experimental model of renal proximal tubular cells in which CT affects Na(+)-Pi cotransport would be useful for examining the mechanisms of this effect. This study evaluated the effect of CT on Na(+)-Pi cotransport in opossum kidney (OK) cells. CT had no effect on Na(+)-Pi cotransport in wild-type OK cells and in the OK-B, OK-H, and OK-P subclones. In contrast, CT at physiological concentrations stimulated Na(+)-Pi cotransport in the OK-7A subclone; the effect was dose related with a 52% increase at 10(-11) M CT, as well as a maximal twofold stimulation at 10(-9) M. CT (10(-11) M) increased the maximum uptake for Na(+)-Pi cotransport (Vmax = 3.55 +/- 0.16 vs. 2.51 +/- 0.17 nmol.mg protein-1.5 min-1, P < 0.01), without affecting the apparent Michaelis constant (Km = 30.6 +/- 1.0 vs. 30.8 +/- 0.7 microM). The stimulatory effect on Na(+)-Pi cotransport was specific for CT and did not occur with 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 1 beta,25-dihydroxyvitamin D3. At 10(-11) M CT, the stimulation of Na(+)-Pi uptake in OK-7A cells was maximal at 3 h; it was completely abolished by preincubation with actinomycin D or cycloheximide. Both calphostin C, an inhibitor of protein kinase C (PKC), or prolonged incubation with phorbol 12-myristate 13-acetate, to downregulate the PKC pathway, partially inhibited the stimulatory effect of CT on Na(+)-Pi cotransport in OK-7A cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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    Keywords

  • Animals, Calcitriol, Clone Cells, Cycloheximide, Dactinomycin, Ion Transport, Kidney, Kinetics, Naphthalenes, Opossums, Parathyroid Hormone, Phosphates, Polycyclic Compounds, Protein Kinase C, Sodium, Tetradecanoylphorbol Acetate, Vitamin D
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    Author List

  • Allon M; Parris M
  • Start Page

  • F404
  • End Page

  • F410
  • Volume

  • 264
  • Issue

  • 3 Pt 2