Investigation of bioactive NO-scavenging role of myoglobin in myocardium

Because nitric oxide (NO) can react with myoglobin (Mb) to oxidize the heme Fe(II) to Fe(III), the appearance of metmyoglobin (metMb) during bradykinin stimulation underpins the hypothesis that Mb acts as an NO scavenger in the cell. Although some experiments have detected the reporter metMb signal in the -3.7 ppm spectral region, others have not corroborated the finding. Because metMb also has characteristic hyperfine-shifted signals in the 40-100 ppm spectral region, detection of these signals would confirm the presence of metMb. Perfused rat myocardium study has examined this spectral region in a range of bradykinin infusion protocols. Although bradykinin elicits a set of physiological responses, consistent with the induction of NO, the ¹H nuclear magnetic resonance spectra in all experiments reveal no detectable metMb signals. Moreover, in the perfused myocardium model, the bradykinin-induced decline in myocardial oxygen consumption does not appear to arise only from NO binding to cytochrome oxidase.