Acute Oxygen Sensing Mechanisms

At birth, associated with the rise in oxygen levels, the resistance pulmonary arteries (PA) dilate and the ductus arteriosus (DA) constricts. In neonatal and adult life, hypoxia in the small airways causes pulmonary vasoconstriction (HPV) which helps to direct mixed venous blood away from poorly ventilated alveolae. HPV and normoxic contraction of the DA both involve at least three different mechanisms that combine to cause smooth muscle cell contraction. These are: Inhibition of the outward potassium current across the cell membrane, resulting in membrane depolarization and calcium entry through L-type calcium channels; release of calcium from the sarcoplasmic reticulum and repletion through the store-operated channels; and calcium-sensitization, in both PA and DA, the change in oxygen tension stimulates Rho kinase, which inhibits myosin light-chain phosphatase and potentiates contraction.