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 cond itions. STUDY DESIGN: Isometric tension and intracellular membrane potential of nat ive (n = 7) and endothelium-denuded (n = 7) human umbilical vein strips wer e 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 membr ane depolarization from -58.2 +/- 1.3 mV (SEM) to -54.0 +/- 0.7 mV (P < .00 9) and increased isometric tension from 0.576 +/- 0.016 g to 0.790 +/- 0.03 2 g (P < .0001). The steepest increase in tension (Delta = 0.063 g) occurre d within the physiologic intrauterine oxygen tension range (27-35 mm Hg). I sometric tension at hypoxia (partial oxygen pressure, 5 mm Hg) corresponded to 88% of resting tension. Tension and membrane potential were related lin early (r(2) = 0.99). Disruption of the endothelium reversed the effects of oxygen pressure. CONCLUSION: Human umbilical vein vascular tone was regulated by oxygen tens ion and showed a hypoxic vasodilator reserve. Oxygen-dependent effects were related to the membrane potential and required the endothelium.