Various substrates have been reported to influence the recovery of hearts upon reperfusion following ischaemia, e.g. pyruvate improves recovery whereas fatty acids appear to be deleterious (Stanley et al. 1997). Glucose oxidation also appears to improve recovery, although high glycolytic rates have been associated with cardiac dysfunction, even though glycolytic ATP has been suggested to provide energy preferentially for ion channel regulation (Losito et al. 1998). In ischaemic hearts, therefore, the improved recovery with pyruvate upon reperfusion may depend also on metabolism of endogenous glycogen, or addition of exogenous glucose. Single cells provide a good model of reperfusion injury, and cell contractile recovery can be monitored together with mitochondrial membrane potential, an indicator of the oxidative capacity of the cell. In this study we investigated the effect of glucose (glu) and/or pyruvate (pyr) on mitochondrial membrane potential (ΔC{special}_m) and cell contraction following metabolic inhibition of adult rat ventricular myocytes.

Adult male rats were humanely killed by cervical dislocation, and myocytes isolated by collagenase digestion. Metabolic inhibition was induced by superfusing cells in buffer containing 2.5 mM NaCN and no substrate at 37 °C. ‘Reperfusion’ was simulated by return to oxygenated buffer containing 16 mM glu and/or 5 mM pyr. ΔC{special}_m was measured using the fluorescent indicator rhodamine 123, and cells were electrically stimulated to contract at 3 Hz. Contraction was measured using an edge-tracking device. Results are expressed as means ± S.D., and statistical significance determined using Student’s t test (paired where appropriate).

Following induction of MI, cells underwent contractile failure (CF) after approximately 15 min (the time varied slightly for each cell), and were reperfused immediately. Myocytes reperfused with glucose recovered contractile ability, although with a smaller amplitude of contraction: 2.8 ± 1.3 vs. 4.7 ± 0.9 % (n = 7, P < 0.05), and ΔC{special}_m was not different from initial values. Very similar results were observed in the presence of both glu and pyr. However, reperfusion with pyruvate alone caused depolarisation of ΔC{special}_m, as indicated by a fluorescence increase to 139 ± 8 % (n = 4, P < 0.02) of initial values. Myocytes did not recover any contractile ability, and underwent rigor contracture. These results suggest that glucose metabolism is necessary for recovery of ΔC{special}_m and cell contraction upon reperfusion, and that, in this model, pyruvate provides no additional protection. Whether glycolysis alone is sufficient for restoration of ΔC{special}_m remains to be investigated.

This work was supported by the British Heart Foundation and BBSRC.