Chronic and acute exposure of mouse hearts to fatty acids increases oxygen cost of excitation-contraction coupling

Abstract

The aim of the present study was to evaluate the underlying processes involved in the oxygen wasting induced by inotropic drugs and acute and chronic elevation of fatty acid (FA) supply, using unloaded perfused mouse hearts from normal and type 2 diabetic (db/db) mice. We found that an acute elevation of the FA supply in normal hearts, as well as a chronic (in vivo) exposure to elevated FA as in db/db hearts, increased myocardial oxygen consumption (MVo₂(unloaded)) due to increased oxygen cost for basal metabolism and for excitation-contraction (EC) coupling. Isoproterenol stimulation, on top of a high FA supply, led to an additive increase in MVo₂(unloaded), because of a further increase in oxygen cost for EC coupling. In db/db hearts, the acute elevation of FA did not further increase MVo₂. Since the elevation in the FA supply is accompanied by increased rates of myocardial FA oxidation, the present study compared MVo₂ following increased FA load versus FA oxidation rate by exposing normal hearts to normal and high FA concentration (NF and HF, respectively) and to compounds that either stimulate (GW-610742) or inhibit [dichloroacetate (DCA)] FA oxidation. While HF and NF + GW-610742 increased FA oxidation to the same extent, only HF increased MVo₂(unloaded). Although DCA counteracted the HF-induced increase in FA oxidation, DCA did not reduce MVo₂(unloaded). Thus, in normal hearts, acute FA-induced oxygen waste is 1) due to an increase in the oxygen cost for both basal metabolism and EC coupling and 2) not dependent on the myocardial FA oxidation rate per se, but on processes initiated by the presence of FAs. In diabetic hearts, chronic exposure to elevated circulating FAs leads to adaptations that afford protection against the detrimental effect of an acute FA load, suggesting different underlying mechanisms behind the increased MVo₂ following acute and chronic FA load.