Mitochondrial
ATP production is continually adjusted to energy demand through coordinated increases in oxidative phosphorylation and
NADH production mediated by mitochondrial Ca2+([Ca2+]m). Elevated cytosolic Na+ impairs [Ca2+]m accumulation during rapid pacing of myocytes, resulting in a decrease in
NADH/NAD+ redox potential. Here, we determined 1) if accentuating [Ca2+]m accumulation prevents the impaired
NADH response at high [Na+]i; 2) if [Ca2+]m handling and
NADH/NAD+ balance during stimulation is impaired with
heart failure (induced by aortic constriction); and 3) if inhibiting [Ca2+]m efflux improves
NADH/NAD+ balance in
heart failure. [Ca2+]m and
NADH were recorded in cells at rest and during voltage clamp stimulation (4Hz) with either 5 or 15 mmol/L [Na+]i. Fast [Ca2+]m transients and a rise in diastolic [Ca2+]m were observed during electric stimulation. [Ca2+]m accumulation was [Na+]i-dependent; less [Ca2+]m accumulated in cells with 15 Na+ versus 5 mmol/L Na+ and
NADH oxidation was evident at 15 mmol/L Na+, but not at 5 mmol/L Na+. Treatment with either the mitochondrial Na+/Ca2+ exchange inhibitor
CGP-37157 (1 micromol/L) or raising cytosolic Pi (2 mmol/L) enhanced [Ca2+]m accumulation and prevented the
NADH oxidation at 15 mmol/L [Na+]i. In
heart failure myocytes, resting [Na+]i increased from 5.2+/-1.4 to 16.8+/-3.1mmol/L and net
NADH oxidation was observed during pacing, whereas
NADH was well matched in controls. Treatment with
CGP-37157 or lowering [Na+]i prevented the impaired
NADH response in
heart failure. We conclude that high [Na+]i (at levels observed in
heart failure) has detrimental effects on mitochondrial bioenergetics, and this impairment can be prevented by inhibiting the mitochondrial Na+/Ca2+ exchanger.