Isoflurane applied during ischemia enhances intracellular calcium accumulation in ventricular myocytes in part by reactive oxygen species.
BACKGROUND
Isoflurane applied before myocardial ischemia has a beneficial preconditioning effect which involves generation of reactive oxygen species (ROS); ROS, however, have been implicated in critical cytosolic calcium ([Ca2+]i) overload during ischemia. We therefore investigated isoflurane's effects on intracellular Ca2+ handling in ischemic ventricular myocytes and the association with ROS.


METHODS
Simulated ischemia was induced in electrically stimulated rat ventricular myocytes for 30 min (ischemia). Isoflurane-treated cells were additionally exposed to 1MAC of isoflurane (ischemia + iso). To determine the contribution of ROS to Ca2+ homeostasis during ischemia in both groups, the intracellular ROS scavenger, N-mercaptopropionylglycine (MPG), was added to the superfusion buffer. The fluorescent ratiometric Ca2+ dye fura-2 was employed to determine [Ca2+]i.


RESULTS
Resting and peak [Ca2+]i increased in the ischemia and the ischemia + iso group. However, Ca2+ accumulation was most prominent in isoflurane-treated cardiomyocytes (P < 0.05) and could be mitigated by MPG in both groups (P < 0.001). Isoflurane also decreased the rate constant of the Ca2+ transient decline but did not further diminish the amplitude of the transient during ischemia.


CONCLUSIONS
Isoflurane when applied during ischemia appears to worsen [Ca2+]i overload, which is caused by impeding Ca2+ clearance. As MPG mitigated the increase in [Ca2+]i, isoflurane seems to enhance ROS-mediated effects on intracellular Ca2+ handling in cellular ischemia.
Dworschak
M
M
Department of Anesthesiology and Intensive Care, Division of Cardiothoracic and Vascular Anesthesia and Intensive Care, University Hospital Vienna, Vienna, Austria. martin.dworschak@univie.ac.at
Breukelmann
D
D
Hannon
J D
JD
D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D005456:Fluorescent Dyes / Q000008:administration & dosage; D016257:Fura-2 / Q000008:administration & dosage / Q000031:analogs & derivatives*; D006321:Heart / Q000187:drug effects; D007424:Intracellular Fluid / Q000378:metabolism; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D017202:Myocardial Ischemia / Q000188:drug therapy*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013997:Time Factors
D018685:Anesthetics, Inhalation; D005456:Fluorescent Dyes; D017382:Reactive Oxygen Species; C049925:fura-2-am; D007530:Isoflurane; D002118:Calcium; D016257:Fura-2