Oxygen-dependent regulation of membrane potential and vascular tone of human umbilical vein, ,

Objective: We question the hypothesis that vascular tone of human umbilical vein is insensitive to oxygen pressure and minimal already at resting conditions. Study Design: Isometric tension and intracellular membrane potential of native (n = 7) and endothelium-denuded (n = 7) human umbilical vein strips were recorded simultaneously at oxygen pressure values of 5 to 104 mm Hg. Results: Increasing oxygen pressure from 5 to 104 mm Hg led to graded membrane depolarization from –58.2 ± 1.3 mV (SEM) to –54.0 ± 0.7 mV (P< .009) and increased isometric tension from 0.576 ± 0.016 g to 0.790 ± 0.032 g (P< .0001). The steepest increase in tension (Δ = 0.063 g) occurred within the physiologic intrauterine oxygen tension range (27-35 mm Hg). Isometric tension at hypoxia (partial oxygen pressure, 5 mm Hg) corresponded to 88% of resting tension. Tension and membrane potential were related linearly (r2 = 0.99). Disruption of the endothelium reversed the effects of oxygen pressure. Conclusion: Human umbilical vein vascular tone was regulated by oxygen tension and showed a hypoxic vasodilator reserve. Oxygen-dependent effects were related to the membrane potential and required the endothelium. (Am J Obstet Gynecol 1999;181:696-700.)