Increase of cardiac work is associated with decrease of mitochondrial NADH

Abstract

In this study we investigated the effect of work and substrate supply on mitochondrial NADH/NAD+ using epicardial autofluorescence in rat hearts perfused according to Langendorff. To avoid vasoconstrictor effects during high work output, nitroprusside-containing Tyrode solution was used. Photobleaching was avoided by using discontinuous ultraviolet excitation for NADH fluorescence measurements. To increase work, heartbeat rate was raised from 5 to 7 Hz, and concomitantly left ventricular pressure was raised stepwise from 0 to +/- 90 mmHg. During substrate-limited (5.5 mM glucose) perfusions, increase in O2 consumption (3.5 +/- 0.4 mumol.min-1.g-1, mean +/- SE, n = 6) caused by increase of heartbeat rate was associated with a significant decrease of NADH fluorescence (-31 +/- 2.5%, mean +/- SE, n = 6). During perfusions with 10 mM pyruvate increase of O2 consumption (3.6 +/- 0.7 mumol.min-1.g-1, mean +/- SE, n = 6) was associated with significant decrease of NADH fluorescence (-20 +/- 2.6%, mean +/- SE, n = 6). These results suggest that a rise in mitochondrial NADH/NAD+ is not the primary stimulus for increase in respiration and that changes of mitochondrial NADH/NAD+ are secondary to changes in O2 consumption.

NADH changes during hypoxia, ischemia, and increased work differ between isolated heart preparations

“…Blood flow can increase with increasing heart rate to keep tissue adequately perfused (15,19,29). Inclusion of a vasodilator such as nitroprusside and fatty acids such as palmitate may prove better at simulating in vivo conditions with an ex vivo working heart preparation and could improve overall function (2).…”

“…Oxygen can be a limiting factor in heart tissue that becomes ischemic and/or hypoxic, and insufficient oxygen availability can lead to an accumulation of NADH. Demand-induced ischemia may also occur during an episode of tacchycardia, when a fast heart rate is accompanied by a drop in aortic pressure that is inadequate for full coronary perfusion (23,30).Fluorescent imaging of epicardial NADH (fNADH) has been demonstrated as a useful tool to gain insight into the redox state of cardiac tissue (1,2,14,15,17,18,20). However, the effect of heart preparation on fNADH within the context of myocardial work load and oxygen supply is not well understood.…”

“…Fluorescent imaging of epicardial NADH (fNADH) has been demonstrated as a useful tool to gain insight into the redox state of cardiac tissue (1,2,14,15,17,18,20). However, the effect of heart preparation on fNADH within the context of myocardial work load and oxygen supply is not well understood.…”

NADH Fluorescence Imaging of Isolated Biventricular Working Rabbit Hearts

“…One way to compare NADH datasets (fNADH(i,j,t)) between experiments is to normalize each fluorescence image using a reference image (fNADH(i,j,t 0 )) from the dataset 9 , as shown in the equation below. Another way to normalize NADH fluorescence is to place a small piece of uranyl glass in the field of view before the experiment 9,18,19 . Uranyl glass will fluorescence (450 -550 nm) when illuminated with UV light to provide a signal that can be used as a stable reference.…”

Regulation of Mitochondrial [NADH] by Cytosolic [Ca 2+ ] and Work in Trabeculae From Hypertrophic and Normal Rat Hearts

“…Because N385 and N456 gradually decreased during the experimental protocols and at different rates, 10,18 Nratio was normalized relative to its value at a pacing frequency of 0.25 Hz (control value). The ratio was further calibrated by assuming a minimum (maximally oxidized) value of [NADH] m corresponding to an Nratio of 0.49 (at 1 Hz).…”