title: Calcitriol stimulates Na(+)-Pi cotransport in a subclone of opossum kidney cells (OK-7A) by a genomic mechanism.
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)
authors.affiliation: Nephrology Research and Training Center, University of Alabama, Birmingham 35294.
authors.forename: M
authors.initials: M
authors.lastname: Allon
authors.forename: M
authors.initials: M
authors.lastname: Parris
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002999:Clone Cells; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D009281:Naphthalenes; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology; D010710:Phosphates / Q000008:administration & dosage / Q000378:metabolism*; D011083:Polycyclic Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D012964:Sodium / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014807:Vitamin D / Q000494:pharmacology
chemical_list: D009281:Naphthalenes; D010281:Parathyroid Hormone; D010710:Phosphates; D011083:Polycyclic Compounds; D014807:Vitamin D; D003609:Dactinomycin; D003513:Cycloheximide; D012964:Sodium; D011493:Protein Kinase C; D002117:Calcitriol; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate