Oxygen causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel.
At birth, pulmonary vasodilation occurs as air-breathing life begins. The mechanism of O2-induced pulmonary vasodilation is unknown. We proposed that O2 causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel (KCa) via a cyclic nucleotide-dependent kinase. We tested this hypothesis in hemodynamic studies in acutely prepared fetal lambs and in patch-clamp studies on resistance fetal pulmonary artery smooth muscle cells. Fetal O2 tension (PaO2) was increased by ventilating the ewe with 100% O2, causing fetal total pulmonary resistance to decrease from 1.18 +/- 0.14 to 0.41 +/- 0.03 mmHg per ml per min. Tetraethylammonium and iberiotoxin, preferential KCa-channel inhibitors, attenuated O2-induced fetal pulmonary vasodilation, while glibenclamide, an ATP-sensitive K+-channel antagonist, had no effect. Treatment with either a guanylate cyclase antagonist (LY83583) or cyclic nucleotide-dependent kinase inhibitors (H-89 and KT 5823) significantly attenuated O2-induced fetal pulmonary vasodilation. Under hypoxic conditions (PaO2 = 25 mmHg), whole-cell K+-channel currents (Ik) were small and were inhibited by 1 mM tetraethylammonium or 100 nM charybdotoxin (CTX; a specific KCa-channel blocker). Normoxia (PaO2 = 120 mmHg) increased Ik by more than 300%, and this was reversed by 100 nM CTX. Nitric oxide also increased Ik. Resting membrane potential was -37.2 +/- 1.9 mV and cells depolarized on exposure to CTX, while hyperpolarizing in normoxia. We conclude that O2 causes fetal pulmonary vasodilation by stimulating a cyclic nucleotide-dependent kinase, resulting in KCa-channel activation, membrane hyperpolarization, and vasodilation.
Cornfield
D N
DN
Department of Pediatrics, University of Minnesota School of Medicine, Minneapolis 55455, USA.
Reeve
H L
HL
Tolarova
S
S
Weir
E K
EK
Archer
S
S
D000470:Alkaloids / Q000494:pharmacology; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D002227:Carbazoles; D018999:Charybdotoxin / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005333:Fetus; D005905:Glyburide / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D000860:Hypoxia; D007211:Indoles; D007546:Isoquinolines / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008955:Models, Cardiovascular; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000196:embryology / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D011247:Pregnancy; D047428:Protein Kinase Inhibitors; D011651:Pulmonary Artery / Q000187:drug effects / Q000196:embryology / Q000502:physiology*; D012756:Sheep; D013449:Sulfonamides; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D000470:Alkaloids; D000634:Aminoquinolines; D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; D007546:Isoquinolines; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; C073601:KT 5823; D009569:Nitric Oxide; D019789:Tetraethylammonium; C064719:iberiotoxin; C041715:6-anilino-5,8-quinolinedione; D019001:Nitric Oxide Synthase; D006162:Guanylate Cyclase; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D010100:Oxygen; D005905:Glyburide