This editorial refers to 'The heart requires glycerol as an energy substrate through aquaporin 7, a glycerol facilitator' by T. Hibuse et al., this issue. Deprivation of available energy has been postulated to play a major role in the genesis of heart failure, 1-3 and accumulating evidence points to the premise that changes in gene expression that alter energy metabolism weaken the heart muscle, 4,5 reinforcing the logic of ameliorating energy substrates, and/or metabolism as a heart failure

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... rapeutic. Reduced cardiac energy levels, in turn, influence a plethora of cardiac events, including free radical defense mechanisms which lower cardiomyocyte survivability, 6 cardiac contractility, 7 adverse remodelling and arrhythmogenic susceptibility. 8 The heart is able to produce energy from a wide range of substrates and shifts continuously between sources, according to supply availability as controlled by exercise, nutritional status, or pathophysiological conditions. Therefore, the immediate cardiac capacity to produce energy and to adapt its metabolism to requirement changes is a crucial cardiac functional parameter. ATP is the direct source of energy for all energy-consuming reactions in the heart (pump function, Ca 2þ re-uptake into the sarcoplasmic reticulum and maintenance of the sarcolemmal ion gradients). In the healthy adult heart, more than 70% of the energy required is covered by fatty acid oxidation in mitochondria, with the remaining 30% being accounted for by carbohydrate oxidation, mainly using glucose and ketone bodies as exogenous substrates. [9] [10] [11] Under conditions of high ATP demand relative to ATP availability, the myocyte is able to recruit additional pathways or depend more heavily on alternative pathways for ATP synthesis (e.g. glycolysis and phosphotransferase reactions). The efficiency of ATP generation differs depending on the oxidized substrates, with fatty acid oxidation generating more ATP, on a molar basis, than glucose utilization. 12 Accumulating evidence indicates that glycerol could be an as of yet largely overlooked metabolic cardiac substrate. [13] [14] [15] In cardiomyocytes, glycerol controls several steps of lipid metabolism by forming a backbone for complex lipid * Corresponding author. Tel: þ31 30 253 8900; fax: þ31 30 253 9036.