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+];) 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 depolarizationinduced rise in [Ca2+] . 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+] . NO (-3 ,uM) and the NO-generating compound sodium nitroprusside (5-10 J,M) opened Kv channels in rat pulmonary artery smooth muscle cells. The enhanced K+ currents then hyperpolarized the cells, and blocked Ca2+-dependent action potentials, thereby preventing the evoked increases in [Ca2+],. 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+1], is apparently one of the mechanisms by which NO induces pulmonary vasodilation.Endothelium-derived relaxing factor, which was first described by Furchgott and Zawadzki in 1980 (1), plays an important role in controlling vascular tone. NO, the best characterized endothelium-derived relaxing factor (2, 3), can be produced by both vascular endothelium and smooth muscle cells (4). Basal release of endothelium-derived NO may help to maintain low resting pulmonary vascular tone in normal humans (4, 5). Dysfunction of endothelial NO production and release is believed to be a major cause of pulmonary hypertension and its sequelae (6, 7). Inhaled NO selectively causes pulmonary vasodilation in patients with pulmonary hypertension (8, 9).The cellular mechanisms of NO-induced pulmonary vasodilation are not completely understood. They apparently involve an increase of intracellular cGMP (10,11) MATERIALS AND METHODS Cell Preparation. Rat PASMC primary cultured for 3-7 days were used for this study. Details of the methods used for isolation and culture of PASMC are published (25). Briefly, the intrapulmonary arterial branches (3rd and 4th order) as well as the right and left branches (2nd order) of rat main PA were incubated for 20 min in Hanks' balanced salt solution containing collagenase (1.5 mg/ml; Worthington). Adventitia and endothelium were removed after incubation. The PA smooth muscle was then digested with 1.5 mg/ml collagenase, 0.5 mg/ml elas...

Voltage-dependent K+ channels regulate the duration of reactive hyperemia in the canine coronary circulation

“…We extend those findings with in vivo studies and demonstrate that adenosine-activated channels are correolide sensitive, and thus contain subunits of the K V 1 family. Similarly, our data support previous studies showing that 4-AP-sensitive K V channels mediate NO-induced vasodilation (33,34,49,50,59). We enhance the understanding of K V channels regulated by NO by demonstrating that they contain correolide-sensitive K V 1 subunits.…”

MLCK and PKC Involvements via Gi and Rho A Protein in Contraction by the Electrical Field Stimulation in Feline Esophageal Smooth Muscle

“…In particular, the 4-AP-induced inhibition of K ＋ channels depolarizes pulmonary arterial smooth muscle cells and then causes vasoconstriction [33]. In addition, NO reportedly plays a role as an activator of Kv channels, which results in hyperpolarization and induces vasodilation in pulmonary arteries and in the opossum esophagus [21,34]. In the present study, although 4-AP did not significantly enhance EFS-induced off-contraction, this contraction was found to increase in a concentration-dependent manner.…”

KvChannels Contribute to Nitric Oxide- and Atrial Natriuretic Peptide-Induced Relaxation of a Rat Conduit Artery

“…Whether K v 2.1 subunit protein forms heteromultimers with K v 2.2 or with other subunits has yet to be determined. Because the relaxations of rat aorta in response to NTG and NOR 3 were almost abolished by the inhibitor of soluble guanylyl cyclase ODQ (Table 2), cGMPdependent rather than cGMP-independent pathway (e.g., NO-direct action) (Yuan et al, 1996;Zhao et al, 1997) is likely to be the primary mechanism for the relaxant response in rat aorta.…”