Effect of cyanide on oxygen tension-dependent mechanical tension in rabbit aorta.

We determined relationships between oxygen uptake and mechanical tension in isolated strips of rabbit aorta treated with various agonists; organ bath Poi was varied over the range 4-350 mm Hg, or cyanide (CN) was added to the organ bath in concentrations of from 8 x 10"' to 3 x 10" J M. Oxygen tension-dependent mechanical tension changes were similar during contractions caused by norepinephrine and angiotensin.During norepinephrine contractions, relaxations resulting from CN were much smaller than those resulting from decreases in organ bath Poi at equivalent rates of oxygen uptake.This effect could not be explained by nonspecific CN effects, which caused relaxation of mechanical tension.The threshold fall in oxygen uptake rate fv"oj) for a fall in mechanical tension was larger with graded CN than with graded hypoxia-Under conditions in which measurable oxygen uptakes by the strips were completely inhibited with CN or maximally inhibited with antimycin A, and tissue Poi was expected to be equilibrated or nearly equilibrated with organ bath Poi, mechanical tension changes were seen with changes in Pot over the range 4-80 mm Hg.These data are consistent with a postulate that an Oj sensor other than cytochrome a is involved in the mechanism of oxygen tension-dependent mechanical tension, although inhibition of the respiratory chain may explain some oxygen tension-dependent mechanical tension.During K + contractions, hypoxic decreases in mechanical tension were much smaller than those seen during norepinephrine or angiotensin contractions.This finding does not give information about the oxygen sensor involved, but the K + contraction preparation is useful in control experiments.The finding that there was no difference in mechanical tension-oxygen uptake plots with CN and with hypoxia during K + contractions, and with CN in norepinephrine contractions, suggests that effects of CN on tension may result from inhibition of the respiratory chain, and strengthens the conclusion that hypoxic relaxations during norepinephrine contractions may be initiated by a mechanism independent of respiratory chain activity.Cine Res 44: 368-378, 1979 IT HAS BEEN SHOWN that "active" mechanical tension in rabbit aorta and other arterial smooth muscles is sensitive to oxygen tension changes (Grubb and Coburn, 1976;Carrier et al., 1964;Detar and Bohr, 1968;Fay, 1971;Pittman and Duling, 1973;Smith and Vane, 1966).There is some evidence obtained for the neonatal guinea pig ductus arteriosus (Fay, 1971;Fay and Jobsis, 1972), and based on measurements of aia 3 spectra, carbon monoxide photodissociation, and other approaches, that cytochrome oxidase is the 0 2 sensor involved in this phenomenon.In the present study, we attempted, using rabbit aorta, to obtain further evidence in support of or against the cytochrome oxidase sensor hypothesis.The "critical" organ bath Po? (OBPO 2 ) for an effect on mechanical tension in vascular smooth