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 α1 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 ∼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 α1 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.
Footnotes
- Received February 14, 1997.
- Accepted March 27, 1997.
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Send reprint requests to: Dr. Carlos H. Pedemonte, University of Houston, Calhoun 4800, Houston, TX 77204–5515. E-mail:pedemonte{at}jetson.uh.edu
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This work was supported by grants from the National Science Foundation (C.H.P.) and the National Institutes of Health [DK52273 (C.H.P.), RR19799 (T.A.P.), and DC01804 (A.R.C.)] and a limited grant-in-aid from the University of Houston (C.H.P.).
- The American Society for Pharmacology and Experimental Therapeutics
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