Regulation of mitochondrial [NADH] by cytosolic [Ca2+] 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 [Ca2+] ([Ca2+]c). The hearts from banded rats developed hypertrophy (heart-to-body weight ratio increased from 4.1+/-0.1 to 4.9+/-0.1 mg/g) and hypertension (systolic arterial pressure increased from 117+/-4 to 175+/-5 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 Ca2+-independent initial fall was larger for trabeculae from rats with hypertrophied hearts than from control rats (eg, 17+/-2% versus 11+/-1% when work was increased by increasing the frequency from 0.25 to 1 Hz). At 1 Hz, average [Ca2+]c was approximately 280 nmol/L, and the Ca2+-dependent [NADH]m recovery was larger for trabeculae from rats with hypertrophied hearts (17+/-4% versus 10+/-2%) despite similar average [Ca2+]c. At steady state after Ca2+-dependent recovery, there was no difference in [NADH]m (fall of 1+/-2% versus 1+/-1%). Furthermore, the Ca2+-dependent overshoot was larger for trabeculae from hypertrophied than from control hearts (increase of 14+/-2% versus 9+/-2% 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 Ca2+-dependent recovery mechanism is enhanced in hypertrophy (because NADH recovered and overshot more), thus compensating for the larger imbalance.
Brandes
R
R
Department of Physiology, Loyola University-Chicago, School of Medicine, Maywood, Ill 60153, USA. rbrande@luc.edu
Maier
L S
LS
Bers
D M
DM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006332:Cardiomegaly / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D003971:Diastole / Q000502:physiology; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004594:Electrophysiology; D005456:Fluorescent Dyes; D006973:Hypertension / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D009210:Myofibrils / Q000378:metabolism; D009243:NAD / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013599:Systole / Q000502:physiology
D005456:Fluorescent Dyes; D007211:Indoles; D009243:NAD; D000255:Adenosine Triphosphate; C048960:indo-1; D002118:Calcium