title: Stimulation of protein kinase C rapidly reduces intracellular Na+ concentration via activation of the Na+ pump in OK cells.
abstract: Na+ reabsorption is regulated in proximal tubules by hormones that stimulate protein kinase C (PKC). To determine whether stimulation of PKC causes a reduction in intracellular Na+ concentration ([Na+]i) that might link Na+ pump activation to increased Na+ reabsorption, [Na+]i was measured in kidney cells loaded with the Na+-sensitive fluorescent indicator SBFI. Rapid digital imaging fluorescence microscopy determinations were performed in epithelial kidney cells transfected with the rodent Na+ pump alpha1 cDNA. In 42 determinations, the basal [Na+]i was 19.7 +/- 2.4 mM. Stimulation of PKC reduced the [Na+]i to 5.6 +/- 0.6 mM in approximately 10 sec. This drastic change in [Na+]i requires a transient 74-120-fold increase in Na+ pump activity. After the new steady state [Na+]i is reached, the Na+ pump is 58% activated. The entry of Na+ into the cells is not affected by stimulation of PKC; therefore, the reduction in [Na+]i is exclusively dependent on activation of the Na+ pump. Accordingly, PKC stimulation does not affect the [Na+]i of cells expressing a mutant Na+ pump that is not stimulated by PKC. The decrease in [Na+]i observed in cells transfected with the rodent Na+ pump alpha1 cDNA is large and sufficiently fast that it is expected to stimulate rapidly passive Na+-influx into the cells, thereby accounting for the observed PKC-induced stimulation of Na+ reabsorption.
authors.affiliation: College of Pharmacy, University of Houston, Texas 77204-5515, USA. pedemonte@jetson.uh.edu
authors.forename: C H
authors.initials: CH
authors.lastname: Pedemonte
authors.forename: T A
authors.initials: TA
authors.lastname: Pressley
authors.forename: A R
authors.initials: AR
authors.lastname: Cinelli
authors.forename: M F
authors.initials: MF
authors.lastname: Lokhandwala
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D007668:Kidney / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D012964:Sodium; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D013755:Tetradecanoylphorbol Acetate