Heart rates and O2 consumption
Hearts were preperfused with isoproterenol solution for 20 min or with a substrate-free buffer without isoproterenol for 20 min to reduce glycogen content. A 60-min perfusion followed with media containing octanoate, lactate, pyruvate, glucose, and [U-13C3]glycerol. Insulin and/or H2O2 were added in some cases, which are specified below.