Hypoxic pulmonary vasoconstriction reduces perfusion in poorly ventilated regions of the lungs and redistributes perfusion to the well-ventilated areas. It therefore decreases venous admixture and optimizes the oxygenation of arterial blood. It is already present in the foetal period when it contributes to the decrease of the overall pulmonary blood flow. It is accepted today that all mechanism of hypoxic pulmonary vasoconstriction are localized in the pulmonary vascular smooth muscle cells. The mechanisms of cellular oxygen sensing are still obscure. Hypoxia inhibits the potassium channels leading to membrane depolarisation of smooth muscle cells and to the opening of voltage gated calcium channels. Then the influx of calcium ions into cytoplasm is increased. The release from the intracellular Ca2+stores participates also. The rise of free cytoplasmatic calcium induces vascular smooth muscle contraction.

        Key words: hypoxia – potassium channels – intracellular calcium – smooth muscle – membrane potential