Response of cytochrome a,a3 to carbon monoxide in canine hearts with prior infarcts

The effects of moderate levels of carbon monoxide (CO) on the oxidation-reduction state of cytochrome a,a3 (cyt a,a3) were examined in the hearts of twelve dogs with a prior myocardial infarction. Exposure to ten minutes CO produced a carboxyhemoglobin (CO-Hb) level of 9.4%, a level experienced by heavy smokers. Accompanying the exposure to CO, cyt a,a3 became more reduced; 17.4% +/- 4.7%. Exposure to CO was accompanied by an increase of 33% +/- 4% in the rate of cyt a,a3 reduction following occlusion of the left circumflex coronary artery and a decrease of 24% +/- 8% in the rate of cyt a,a3 oxidation with release. There was also a decrease in the magnitude of cyt a,a3 reduction from 86% +/- 9% to 70% +/- 11%. These results indicate that moderate levels of CO trap cyt a,a3 in the reduced state which impairs the ability of the heart to recover from transient ischemic episodes.