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Our laboratory has previously reported evidence that tone responses of isolated endothelium-removed calf pulmonary arteries elicited by changes in PO2 appear to be mediated via changes in H2O2 and guanosine 3',5'-cyclic monophosphate, and that the PO2 sensor mechanism is hypothesized to involve changes in superoxide anion (O2-.) production by a microsomal NADH-oxidoreductase, which is the major source of O2-. detected by lucigenin-elicited chemiluminescence (CL) in this tissue. In this study we examined if the flavoprotein-directed inhibitor of O2-. producing NAD(P)H oxidoreductases, diphenyliodonium (DPI), could be employed as an inhibitor of O2-. production by NADH oxidoreductase, which functions as a selective probe for PO2-elicited tone responses in calf pulmonary arterial smooth muscle. It was found that 1 microM DPI inhibited NADH-dependent production of CL in the arterial smooth muscle homogenate by 49% (n = 10). DPI reduced basal CL from endothelium-removed pulmonary arteries by 41% (n = 15). In endothelium-removed pulmonary arteries precontracted with U-46619, the hypoxic contraction of 2.3 +/- 0.5 g was reduced to 0.1 +/- 0.4 g (n = 7) by DPI, and the reoxygenation relaxation of 32.7 +/- 7.5% was decreased to 4.4 +/- 1.4% (n = 7). DPI did not have any significant effect on U-46619- or K(+)-elicited tone generation. DPI also did not alter the relaxation to H2O2 (1 microM-0.1 mM, n = 6), nitric oxide (0.42 nM-420 nM, n = 12), or isoproterenol (1 nM-1 microM, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
Mohazzab et al. (Wed,) studied this question.