Citrate measurements. Myotubes were incubated 30 min at 37 °C in KRB containing glucose and PAA concentration as stated in the text or figure. Incubation media were collected for citrate measurement and 13% perchloric acid was added to the media. Precipitated proteins were removed by centrifugation, and the supernatants were neutralized by adding 2 N KH2CO3. The precipitated potassium perchlorate salt was eliminated by centrifugation, and the resulting supernatants were stored at −80 °C and subsequently used for citrate measurements. Citrate was assayed by coupling the citrate lyase/malate dehydrogenase (Boehringer Mannheim, Mannheim, Germany) reactions according to Williamson and Corkey [14]. Sample or citrate standard (0.1–2 nmol) was added to 0.1 M Tris–HCl buffer, pH 7.6, 40 μM ZnCl2, 3 μM NADH, 0.4 μg/ml malate dehydrogenase (EC 1.1.1.37), final volume 0.5 ml. Fluorescence was determined at 340 nm excitation and 465 nm emission, then repeated 10 min after adding of citrate lyase (EC 4.1.3.8) solution.