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

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Abstract
Relationships were determined between O2 uptake and mechanical tension in isolated strips of rabbit aorta treated with various agonists; organ bath O2 partial pressure (PO2) was varied over the range 4-350 mm Hg, or cyanide (CN) was added to the organ bath in concentrations of 6 .times. 10-5-3 .times. 10-3 M. O2 tension-dependent mechanical tension changes were similar during contractions caused by norepinephrine and angiotensin. During norepinephrine contractions, relaxations due to CN were smaller than those due to decreased organ bath PO2 at equivalent rates of O2 uptake. This effect could not be explained by nonspecific CN effects, which caused relaxation of mechanical tension. The threshold fall in O2 uptake rate for a fall in mechanical tension was larger with graded CN than with graded hypoxia. Under conditions of measurable O2 uptake by the strips, complete inhibition with CN or maximal inhibition with antimycin A occurred and tissue PO2 was expected to equilibrate or nearly equilibrate with organ bath PO2, and mechanical tension changed with changes in PO2 over the range 4-80 mm Hg. An O2 sensor other than cytochrome a1a3 may be involved in the mechanism of O2 tension-dependent mechanical tension but respiratory chain inhibition may explain some O2 tension-dependent mechanical tension. During K+ contractions, hypoxic decreases in mechanical tension were smaller than those during norepinephrine or angiotensin contractions. The O2 sensor involved was not explained, but K+ contraction preparation was used. Mechanical tension-O2 uptake plots with CN and with hypoxia during K+ contractions and with CN in norepinephrine contractions did not differ, suggesting that CN effects on tension may result from inhibition of the respiratory chain, and hypoxic relaxation during norepinephrine contractions may be initiated by a mechanism independent of respiratory chain activity.

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