Human skeletal muscle PDH kinase activity and isoform expression during a 3-day high-fat/low-carbohydrate diet

The increase in skeletal muscle pyruvate dehydrogenase kinase (PDK) activit y was measured in skeletal muscle of six healthy males after a eucaloric hi gh-fat/low-carbohydrate (HF/LC; 5% carbohydrate, 73% fat, and 22% protein o f total energy intake) diet compared with a standardized prediet (50% carbo hdyrate, 30% fat, and 21% protein). Biopsies were obtained from the vastus lateralis muscle after 3 days on the prediet (day 0) and after 1, 2, and 3 days of the HF/LC diet. Intact mitchondria were extracted from fresh muscle and analyzed for PDK activity and Western blotting of PDK2 and PDK4 protei n. A second biopsy was taken at each time point and frozen for Northern blo t analysis of PDK2 and PDK4 mRNAs. PDK activity increased in a linear fashi on over the 3-day HF/LC diet and was significantly higher than control by 1 day. PDK activity was 0.09 +/-0.03, 0.18 +/-0.05, 0.30 +/-0.07, and 0.37 /-0.09 min(-1) at 0, 1, 2, and 3 days, respectively. PDK4 protein and mRNA increased maximally by day 1, and PDK2 protein and mRNA were unaffected by the HF/LC diet. Resting respiratory exchange ratios decreased after 1 day o f the HF/LC diet (from 0.79 +/-0.02 to 0.72 +/-0.02) and remained depressed throughout the 3-day dietary intervention (0.68 +/-0.01). The immediate sh ift to fat utilization was accompanied by increased blood glycerol, beta -h ydroxybutyrate, and plasma free fatty acid concentrations. These results su ggest that the continuing increase in PDK activity over the 3-day HF/LC die t is not due to increasing PDK protein beyond 1 day. This could be due to t he contribution of another isoform to the total PDK activity or to a contin ual increase in PDK4 or PDK2 specific activity.