Nitric oxide and endothelin in oxygen-dependent regulation of vascular tone of human umbilical vein

We investigated the possible contribution of nitric oxide (NO) and endothelin (ET) to oxygen-dependent regulation of human umbilical vein vascular tone by simultaneous registration of intracellular membrane potential and isometric tension of vessel strips with and without NO synthase inhibition [10–4 M Nω-nitro-l-arginine methyl ester (l-NAME)], ETA receptor blockade (10–5 M BQ-123), or ETB receptor blockade (10–7 M BQ-788) at Po2 values in the bath solution between 5 and 104 mmHg. Increasing Po2 above the physiological intrauterine range resulted in depolarization and an increase of isometric tension, whereas lowering Po2 resulted in hyperpolarization and a decrease in isometric tension. Removal of the endothelium reversed these effects. At Po2 values below 39 mmHg, intact preparations treated with either l-NAME, BQ-788, or BQ-123 were more depolarized than controls. In the case of treatment with l-NAME or BQ-123, this was accompanied by an increase in isometric tension. We conclude that it is NO that me...