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Independent Regulation of In Vivo Insulin Action on Glucose Versus K⁺ Uptake by Dietary Fat and K⁺ Content

From the Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California

Insulin stimulates both glucose and K⁺ uptake, and high-fat feeding is known to decrease insulin-stimulated glucose uptake. The purpose of this study was to examine whether insulin’s actions on glucose and K⁺ uptake are similarly decreased by a high-fat diet. Wistar rats were fed a standard control (12.2% fat; n = 6) or high-fat (66.5% fat; n = 13) diet for 15 days. Because K⁺ content was 1% in the control and 0.5% in the high-fat diet and because the rats ate less of the high-fat diet, we also compared the high-fat diet with 0.5% K⁺ (HFD; n = 7) to a high-fat diet supplemented with 1.5% K⁺ (HFD+K; n = 6). K⁺ intake was matched between the control and HFD+K groups (246 ± 8 vs. 224 ± 2 mg/day), but was lower in the HFD group (78 ± 10 mg/day; P < 0.05). Insulin-stimulated glucose and K⁺ uptake were determined by hyperinsulinemic (5 mU · kg^-1 · min^-1) glucose and K⁺ clamps. The HFD depressed both insulin-stimulated glucose uptake compared to the control (133 ± 5 vs. 166 ± 7 µmol · kg^-1 · min^-1; P < 0.05) and K⁺ uptake (5.5 ± 0.9 vs. 8.9 ± 1.0 µmol · kg^-1 · min^-1; P < 0.05) compared to the control. However, insulin-stimulated K⁺ uptake was unchanged in the HFD+K versus in the control group (10.0 ± 0.6 vs. 8.9 ± 1.0 µmol · kg^-1 · min^-1; P > 0.05), whereas insulin-stimulated glucose uptake in the HFD+K group was decreased to a rate (137 ± 9 µmol · kg^-1 · min^-1), similar to that of the HFD group. We concluded that the decrease in insulin-stimulated K⁺ uptake during high-fat feeding was a result of decreased K⁺ intake, and that insulin’s actions on glucose uptake and K⁺ uptake are independently regulated by dietary fat and K⁺ content, respectively.

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