title: NO hyperpolarizes pulmonary artery smooth muscle cells and decreases the intracellular Ca2+ concentration by activating voltage-gated K+ channels.
abstract: NO causes pulmonary vasodilation in patients with pulmonary hypertension. In pulmonary arterial smooth muscle cells, the activity of voltage-gated K+ (Kv) channels controls resting membrane potential. In turn, membrane potential is an important regulator of the intracellular free calcium concentration ([Ca2+]i) and pulmonary vascular tone. We used patch clamp methods to determine whether the NO-induced pulmonary vasodilation is mediated by activation of Kv channels. Quantitative fluorescence microscopy was employed to test the effect of NO on the depolarization-induced rise in [Ca2+]i. Blockade of Kv channels by 4-aminopyridine (5 mM) depolarized pulmonary artery myocytes to threshold for initiation of Ca2+ action potentials, and thereby increased [Ca2+]i. NO (approximately 3 microM) and the NO-generating compound sodium nitroprusside (5-10 microM) opened Kv channels in rat pulmonary artery smooth muscle cells. The enhanced K+ currents then hyperpolarized the cells, and blocked Ca(2+)-dependent action potentials, thereby preventing the evoked increases in [Ca2+]i. Nitroprusside also increased the probability of Kv channel opening in excised, outside-out membrane patches. This raises the possibility that NO may act either directly on the channel protein or on a closely associated molecule rather than via soluble guanylate cyclase. In isolated pulmonary arteries, 4-aminopyridine significantly inhibited NO-induced relaxation. We conclude that NO promotes the opening of Kv channels in pulmonary arterial smooth muscle cells. The resulting membrane hyperpolarization, which lowers [Ca2+]i, is apparently one of the mechanisms by which NO induces pulmonary vasodilation.
authors.affiliation: Department of Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA. xyuan@umabnet.ab.umd.edu
authors.forename: X J
authors.initials: XJ
authors.lastname: Yuan
authors.forename: M L
authors.initials: ML
authors.lastname: Tod
authors.forename: L J
authors.initials: LJ
authors.lastname: Rubin
authors.forename: M P
authors.initials: MP
authors.lastname: Blaustein
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D015640:Ion Channel Gating; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011651:Pulmonary Artery / Q000502:physiology*; D051381:Rats; D012977:Sodium Nitrite / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects
chemical_list: D015221:Potassium Channels; D009599:Nitroprusside; D009569:Nitric Oxide; D015761:4-Aminopyridine; D012977:Sodium Nitrite; D002118:Calcium