Real-time measurement of energy expenditure in the heart
at the University of Bristol, the University of Cambridge and Imperial College London,
all in the UK, have made real-time measurements of ATP levels in heart cells using
luciferase. Their findings could lead to improved patient recovery from heart attacks
and after heart surgery.
As published in the Journal of Biological Chemistry
on Sept. 22, they incubated heart cells from adult rats with adenoviruses encoding
either cytosolically or mitochondrially targeted luciferase. At various cellular
activity levels, the researchers measured light emission from luciferase. Images
were taken at a rate of 60 fps using an Olympus inverted microscope in time-resolved
imaging mode and a triply intensified CCD camera.
calcium is known to stimulate ATP production, transient calcium signaling in the
mitochondria of adult rat heart cells has not been studied. Therefore, the researchers
also measured calcium levels using aequorin, another light-emitting reporter.
During the contractile cycle, calcium levels
increased in both the cytosol and mitochondria, while ATP levels remained constant.
The researchers said that these findings support the parallel activation model,
whereby cytosolic calcium stimulates ATP use and mitochondrial calcium triggers
ATP production, ensuring that ATP production and use are well-matched.
Under normal conditions, ATP levels
increased rapidly to meet stress demands. However, when the heart cells were stimulated
from rest, ATP levels more slowly returned to sufficient levels. The researchers
said that such an ATP deficiency could prevent the heart from beating properly.
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