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Abstract: TH-OR003

Dietary Fructose Enhances Protein Kinase C Activity and Angiotensin II-Dependent Transport in Proximal Tubules

Session Information

Category: Fluid and Electrolytes

  • 901 Fluid and Electrolytes: Basic

Author

  • Garvin, Jeffrey L., Case Western Reserve University, Cleveland, Ohio, United States
Background

In both humans and model organisms fructose causes salt-sensitive hypertension. This is in part due to increasing the sensitivity of proximal nephron Na reabsorption to angiotensin II (Ang II) such that lower concentrations stimulate transport to a greater extent. Ang II stimulates Na transport in proximal tubules by activating protein kinase C (PKC) α, a calcium- and lipid-dependent kinase.We hypothesized that dietary fructose increases the ability of Ang II to elevate intracellular calcium (Cai) and, thereby, activate PKC α in proximal tubules. This, in turn, stimulates Na/H exchange activity, the primary transporter involved in Na reabsorption.

Methods

Rats were fed a diet of normal chow plus tap water or normal chow plus 20% fructose in drinking water for 7-8 days. The effect of Ang II on Cai was measured using Fura2 in isolated, perfused S2 segments of proximal tubules. Na/H exchange (NHE) activity was measured in perfused tubules using the pH-sensitive dye BCECF. PKC α activity was measured by separating particulate and soluble fractions, performing Western blots and recording the particulate to soluble ratio. Increases in this ratio was taken as activation.

Results

Basal Cai was 143±29 nM in proximal tubules from control rats while it was 160±30 nM in those given fructose, not significantly different. Ang II (1 nM) increased Cai by 43±10 nM in control tubules and by 148±53 nM in tubules from rats fed fructose (p < 0.03). A higher concentration of Ang II (100 nM) increased Cai by 237±100 nM in proximal tubules from rats fed fructose and by 190±34 nM in tubules from rats fed the control diet. Ang II increased the particulate to soluble ratio of PKC α by 0.134±0.026 in tubules from rats fed fructose (p <0.001) but not significantly in control tubules (0.060±0.061). Finally we measured NHE activity. Ang II (1 pM) increased NHE activity by 0.7±0.1 fluorescent units/s in tubules from rats given fructose but had no effect on NHE activity in control tubules (p<0.01). With Go6976, a PKC α/β1 inhibitor, Ang II was unable to stimulate NHE activity in tubules from rats fed fructose.

Conclusion

We concluded that dietary fructose increases the ability of Ang II to elevate Cai, and consequently PKCα. This, in turn, stimulates NHE activity which likely contributes to fructose-induced salt-sensitivity of blood pressure.

Funding

  • Other NIH Support