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Abstract: SA-PO330

The Distal Convoluted Tubule Serves as a Potassium Switch in an Intracellular Chloride-Dependent Mechanism

Session Information

Category: Hypertension and CVD

  • 1403 Hypertension and CVD: Mechanisms

Authors

  • Su, Xiao-Tong, Oregon Health and Science University, Portland, Oregon, United States
  • Klett, Nathan, McGill University, Montreal, Quebec, Canada
  • Allen, Charles N., Oregon Health and Science University, Portland, Oregon, United States
  • Yang, Chao-Ling, Oregon Health and Science University, Portland, Oregon, United States
  • Wang, WenHui, New York Medical College, Portland, Oregon, United States
  • Ellison, David H., Oregon Health and Science University, Portland, Oregon, United States
Background

The kidney plays a key role in the regulation of K+ excretion and K+ homeostasis. Previous studies have demonstrated that the thiazide-sensitive Na-Cl cotransporter (NCC) in the distal convoluted tubule (DCT) plays an important role in the regulation of renal K+ excretion by controlling sodium and volume delivery to the distal nephron. It has been shown that NCC is inhibited when K+ intake is high and activated when dietary K+ intake is low. It is now generally accepted that WNKs (with-no-lysine kinases) plays a major role in NCC phosphorylation and activation. A large body of evidence has demonstrated that WNK1 and WNK4 are chloride-sensitive kinases, which are inhibited by high intracellular chloride concentration ([Cl-]i) and activated by low [Cl-]i. It has also been suggested that membrane voltage changes by extracellular K+ concentrations are responsible for altering the [Cl-]i thereby affecting WNK activity. The aim of our study is to test the hypothesis that changes in the basolateral cell voltage alter the [Cl-]i in the DCT.

Methods

To determine the [Cl-]i in the DCT, we have used isolated single DCT tubule of transgenic mice expressing Cl-sensor, a chloride-sensitive fluorescent protein modified from Chlomeleon. The Cl-sensor contains both a chloride-sensitive YFP moiety as well as a chloride-insensitive CFP moiety, allowing ratiometric estimation of [Cl-]i.

Results

We first measured the [Cl-]i in the isolated DCT by establishing the calibration curve. Using this calibration curve, we estimated that basal DCT [Cl-]i is 6.8 ± 2.3 mM (n=18). Changing the extracellular potassium concentration from 10 mM to 2 mM decreases the [Cl-]i. To test the role of the basolateral Kir4.1/Kir5.1 of the DCT in altering [Cl-]i, we examined whether inhibition of the basolateral K+ channels with Ba2+ would increase the [Cl-]i since Ba2+ has been shown to depolarize DCT membrane. Indeed, Inhibition of Kir4.1/Kir5.1 significantly increased the [Cl-]i in the DCT bathed in a solution containing 2 mM K+.

Conclusion

Our results indicate that the intracellular Cl- concentrations of DCT cells are low at baseline and that the depolarization increases whereas hyperpolarization decreases the intracellular Cl- concentrations. Thus, changes in DCT voltage are associated with alteration of intracellular Cl- concentrations.

Funding

  • NIDDK Support