Continuous measurements of cytoplasmic ATP in single cardiomyocytes during simulation of the "oxygen paradox".
OBJECTIVE
It is now possible to monitor cytoplasmic ATP in single cardiomyocytes and it has recently been shown that cardiomyocytes exposed for several minutes to metabolic inhibitors undergo an abrupt rigor mediated shortening which coincides with a sudden fall in cytoplasmic ATP, from approximately 150 mumol.litre-1 to a few micromolar or less. The objective of this work was to monitor cytoplasmic ATP during simulated reoxygenation of a poisoned cardiomyocyte.


METHODS
Firefly luciferase was injected into a single cell and the light signal generated when luciferin was superfused was monitored. Calibration of the signal is complicated by a transient enhancement of the signal (possibly the result of complex luciferase kinetics), and by uncertainties about cytoplasmic pH.


RESULTS
The data indicate that millimolar levels of cytoplasmic ATP are restored within 1-2 min of cyanide removal.


CONCLUSIONS
Cytoplasmic free calcium is known to rise after poisoned cells undergo shortening, so it is conceivable that the restoration of cytoplasmic ATP in a cell in which free calcium is at micromolar levels may provide a plausible cellular mechanism for the "oxygen paradox". Reoxygenation induces large amplitude, but slow, oscillations in free calcium which, together with the millimolar levels of ATP indicated here, could provide the stimuli for generating the uncoordinated mechanical forces that are prevalent in the oxygen paradox.
Bowers
K C
KC
Department of Human Anatomy and Cell Biology, University of Liverpool, United Kingdom.
Allshire
A P
AP
Cobbold
P H
PH
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D048429:Cell Size / Q000187:drug effects; D003486:Cyanides / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism*; D003847:Deoxyglucose / Q000494:pharmacology; D049454:Firefly Luciferin / Q000494:pharmacology; D008156:Luciferases / Q000494:pharmacology; D008845:Microinjections; D015428:Myocardial Reperfusion Injury / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010477:Perfusion; D051381:Rats
D003486:Cyanides; D049454:Firefly Luciferin; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D008156:Luciferases