Changes in NO bioavailabilty regulate cardiac O2consumption: control by intramitochondrial SOD2 and intracellular myoglobin

Abstract
The aim of this study was to investigate the significance of two intracellular scavengers of nitric oxide (NO): 1) superoxide dismutase (SOD) (SOD2) to scavenge intramitochondrial superoxide anion, and 2) cytosolic myoglobin (Mb) in the regulation of tissue O2consumption. O2consumption was measured in vitro using a Clark-type O2electrode. SOD heterozygous mice (SODHZ) ( n = 13) and SOD wild-type (SODWT) ( n = 5) mice were used. Bradykinin (BK, 10–4mol/l) reduced O2consumption by 15% ± 1 in hearts of SODHZ mice, which was significantly different from SODWT (reduced by 24 ± 0.4%). Tiron significantly increased the inhibition of O2consumption by BK in male mice from 15 ± 1% ( n = 13) to 29 ± 1.2% ( n = 4) at 10–4mol/l concentration ( P < 0.05). The effect of carbachol was similar to BK. S-nitroso- N-acetyl penicillamine (SNAP, 10–4mol/l) reduced O2consumption by 39 ± 1.3% in hearts of SODHZ mice, which was not significantly different from SODWT. But at 10–7mol/l, SNAP caused significantly less inhibition of O2consumption in SODHZ mice. Mb knockout (MbKO; Mb wild-type n = 6) and (MbWT) mice ( n = 6) were also used. Kidney cortex was studied as the negative control because it does not contain Mb. BK (10–4mol/l) reduced O2consumption by 32 ± 2, 29 ± 1, and 26 ± 1% in the heart, skeletal muscle, and kidney of MbKO mice, which was also not significantly different from MbWT. SNAP (10–4mol/l) reduced O2consumption by 39 ± 3, 42 ± 4, and 46 ± 2% in the heart, skeletal muscle, and kidney of MbKO mice, which was also not significantly different from MbWT. NG-nitro-l-arginine methyl ester ( P < 0.05) inhibited the reduction in O2consumption induced by BK in the MbKO mouse heart (15 ± 1%), skeletal muscle (17 ± 1%), and kidney (17 ± 1%) as in the MbWT mice. These results suggest that the role of Mb as an intracellular NO scavenger is small, and the increase in mitochondrial superoxide in SODHZ mice may cause a decrease NO bioavailability and alter the control of myocardial O2consumption by NO.