Regulation of Mitochondrial [NADH] by Cytosolic [Ca] and Work in Trabeculae From Hypertrophic and Normal Rat Hearts

Pressure overload hypertrophy has previously been shown to reduce contractility but paradoxically to increase O2 consumption rates at a given force. Because O2 consumption rates are related to mitochondrial [NADH] ([NADH]m), we tested the hypothesis that with hypertrophy, control of [NADH]m may be altered. Left ventricular trabeculae were isolated from banded and control rat hearts, and fluorescence spectroscopy was used to monitor [NADH]m and cytosolic [Ca] ([Ca]c). The hearts from banded rats developed hypertrophy (heart-to-body weight ratio increased from 4.160.1 to 4.960.1 mg/g) and hypertension (systolic arterial pressure increased from 11764 to 17565 mm Hg). Muscle workload was increased by stepwise increases in pacing frequency (up to 2 Hz). After increased work, [NADH]m fell and then slowly recovered toward control levels. When work was decreased, [NADH]m overshot control values and then slowly returned. The Ca-independent initial fall was larger for trabeculae from rats with hypertrophied hearts than from control rats (eg, 1762% versus 1161% when work was increased by increasing the frequency from 0.25 to 1 Hz). At 1 Hz, average [Ca]c was '280 nmol/L, and the Ca -dependent [NADH]m recovery was larger for trabeculae from rats with hypertrophied hearts (1764% versus 1062%) despite similar average [Ca]c. At steady state after Ca-dependent recovery, there was no difference in [NADH]m (fall of 162% versus 161%). Furthermore, the Ca-dependent overshoot was larger for trabeculae from hypertrophied than from control hearts (increase of 1462% versus 962% when frequency was decreased from 1 to 0.25 Hz). We conclude that (1) there is initially a larger imbalance in NADH production versus consumption rate in hypertrophy (because NADH fell more) and (2) the Ca-dependent recovery mechanism is enhanced in hypertrophy (because NADH recovered and overshot more), thus compensating for the larger imbalance. (Circ Res. 1998;82:1189-1198.)