Valerie A. Porter

Redox Signaling in Oxygen Sensing by Vessels

In response to the increase in oxygen tension at birth, the resistance pulmonary arteries dilate, while the ductus arteriosus constricts. Although modulated by the endothelium, these opposite responses are intrinsic to the vascular smooth muscle. While still controversial, it seems likely that during normoxia the production of reactive oxygen species (ROS) increases and the smooth muscle cell cytoplasm is more oxidized in both pulmonary arteries and ductus, compared to hypoxia. However, the effect of changes in the endogenous redox status or the addition of a redox agent, oxidizing or reducing, is exactly opposite in the two vessels. A reducing agent, dithiothreitol, like hypoxia, in the pulmonary artery will inhibit potassium current, cause depolarization, increase cytosolic calcium and lead to contraction. Responses to dithiothreitol in the ductus are opposite and removal of endogenous H(2)O(2) by intracellular catalase in the ductus increases potassium current. Oxygen sensing in both vessels is probably mediated by redox effects on both calcium influx and calcium release from the sarcoplasmic reticulum (SR).

NO causes perinatal pulmonary vasodilation through K+-channel activation and intracellular Ca2+release

Evidence suggests that nitric oxide (NO) causes perinatal pulmonary vasodilation through K+-channel activation. We hypothesized that this effect worked through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channel that requires release of intracellular Ca2+ from a ryanodine-sensitive store. We studied the effects of 1) K+-channel blockade with tetraethylammonium, 4-aminopyridine, a voltage-dependent K+-channel blocker, or glibenclamide, an ATP-sensitive K+-channel blocker; 2) cyclic nucleotide-sensitive kinase blockade with either KT-5823, a guanylate-sensitive kinase blocker, or H-89, an adenylate-sensitive kinase blocker; and 3) blockade of intracellular Ca2+ release with ryanodine on NO-induced pulmonary vasodilation in acutely prepared late-gestation fetal lambs. N-nitro-L-arginine, a competitive inhibitor of endothelium-derived NO synthase, was infused into the left pulmonary artery, and tracheotomy was placed. The animals were ventilated with 100% oxygen for 20 min, followed by ventilation with 100% oxygen and inhaled NO at 20 parts/million (ppm) for 20 min. This represents the control period. In separate protocols, the animals received an intrapulmonary infusion of the different blockers and were ventilated as above. Tetraethylammonium (n = 6 animals) and KT-5823 (n = 4 animals) attenuated the response, whereas ryanodine (n = 5 animals) blocked NO-induced perinatal pulmonary vasodilation. 4-Aminopyridine (n = 5 animals), glibenclamide (n = 5 animals), and H-89 (n = 4 animals) did not affect NO-induced pulmonary vasodilation. We conclude that NO causes perinatal pulmonary vasodilation through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channels and release of Ca2+ from ryanodine-sensitive stores.Evidence suggests that nitric oxide (NO) causes perinatal pulmonary vasodilation through K+-channel activation. We hypothesized that this effect worked through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channel that requires release of intracellular Ca2+ from a ryanodine-sensitive store. We studied the effects of 1) K+-channel blockade with tetraethylammonium, 4-aminopyridine, a voltage-dependent K+-channel blocker, or glibenclamide, an ATP-sensitive K+-channel blocker; 2) cyclic nucleotide-sensitive kinase blockade with either KT-5823, a guanylate-sensitive kinase blocker, or H-89, an adenylate-sensitive kinase blocker; and 3) blockade of intracellular Ca2+ release with ryanodine on NO-induced pulmonary vasodilation in acutely prepared late-gestation fetal lambs. N-nitro-l-arginine, a competitive inhibitor of endothelium-derived NO synthase, was infused into the left pulmonary artery, and tracheotomy was placed. The animals were ventilated with 100% oxygen for 20 min, followed by ventilation with 100% oxygen and inhaled NO at 20 parts/million (ppm) for 20 min. This represents the control period. In separate protocols, the animals received an intrapulmonary infusion of the different blockers and were ventilated as above. Tetraethylammonium ( n = 6 animals) and KT-5823 ( n = 4 animals) attenuated the response, whereas ryanodine ( n = 5 animals) blocked NO-induced perinatal pulmonary vasodilation. 4-Aminopyridine ( n = 5 animals), glibenclamide ( n = 5 animals), and H-89 ( n = 4 animals) did not affect NO-induced pulmonary vasodilation. We conclude that NO causes perinatal pulmonary vasodilation through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channels and release of Ca2+ from ryanodine-sensitive stores.

Inhaled Nitric Oxide Causes Perinatal Pulmonary Vasodilation Through a Ryanodine-Sensitive Activation of a Kca Channel |[dagger]| 1739

While the normal transition from fetus to newborn requires pulmonary vasodilation mediated by nitric oxide (NO), the mechanism for this remains incompletely understood. Recent evidence suggests that NO acts through K+ channel activation. We hypothesized that NO mediates perinatal pulmonary vasodilation through release of intracellular calcium, from a ryanodine-sensitive store to cause activation of a calcium-sensitive K+ (KCa) channel. To test this hypothesis we studied the effect of: (i) KCa block; (ii) voltage-gated K+ (Kv) channel block; and (iii) blockade of the ryanodine-sensitive store on NO-induced pulmonary vasodilation in acutely prepared, late-gestation fetal lambs (n=5). After a minimum recovery period of one hour, nitro-L-arginine (L-NA, 1 mg/min for 30 min), an NO inhibitor, was infused into the left pulmonary artery (LPA), and tracheotomy placed. Animals were ventilated with 100% O2 for 20 minutes, followed by ventilation with 100% O2 + inhaled NO (iNO) at 20 ppm for 10 minutes. In separate protocols, animals received intrapulmonary infusion of: (i) tetraethylammonium (TEA, 1 mg/min for 50 min), a preferential KCa blocker; (ii) 4-aminopyridine (4-AP, 1 mg/min for 17 min,), a Kv channel blocker; and (iii) ryanodine (5μg/min for 30 min), a blocker of intracellular calcium release, and ventilated as above.

Calcium-Sensitive K+ Channel Activity Controls Basal Cytosolic Ca2+ Concentration and Nitric Oxide Synthase Activity in Fetal Pulmonary Artery Endothelial Cells

Calcium-Sensitive K+ Channel Activity Controls Basal Cytosolic Ca2+ Concentration and Nitric Oxide Synthase Activity in Fetal Pulmonary Artery Endothelial Cells