Oxygen: influence on cyclic nucleotides and calcium sequestration in the human umbilical artery.

and Martha Vaughan, M.D. T he increase in O tension to which the human umbilical artery is exposed at birth acts in at least two separate but related ways to initiate closure of the vessel. Oxygen itself directly induces constriction.’ It plays further a “permissive” role in the action of other chemical agents that cause contraction.’ The relationship between elevated Po and contraction is believed to reflect synthesis of ATP via oxidative phosphorylation.2 However, the availability of ATP to the contractile proteins appears not to be limited to oxidative phosphorylation since in the presence of inhibitors of oxidative phosphorylation adequate ATP is generated by glycolysis and the artery is still capable of developing tension when stimulated by contractile agonists.3 In the experiments reported here we have considered two alternative mechanisms through which Q may control arterial tension: one controlling the active sequestration and uptake of intracellular Ca by subcellular fractions, the other controlling the metabolism of the “second messengers,” cyclic 3’,5’-adenosine monophosphate (cAMP) and cyclic 3’,5’-guanosine monophosphate (cCMP).