Development of a Red-Light-Controllable Nitric Oxide Releaser to Control Smooth Muscle Relaxation in Vivo

Nitric oxide (NO) plays many important physiological roles, including the regulation of vascular smooth muscle tone. In response to hemodynamic or agonist stimuli, endothelial cells produce NO, which can diffuse to smooth muscle where it activates soluble guanylate cyclase (sGC), leading to cGMP formation and smooth muscle relaxation. The close proximity of red blood cells suggests, however, that a significant amount of NO released will be scavenged by blood, and thus the issue of bioavailability of endothelium-derived NO to smooth muscle has been investigated experimentally and theoretically. We formulated a mathematical model for NO transport in an arteriole to test the hypothesis that transient, burst-like NO production can facilitate efficient NO delivery to smooth muscle and reduce NO scavenging by blood. The model simulations predict that 1) the endothelium can maintain a physiologically significant amount of NO in smooth muscle despite the presence of NO scavengers such as hemoglobin and myoglobin; 2) under certain conditions, transient NO release presents a more efficient way for activating sGC and it can increase cGMP formation severalfold; and 3) frequency-rather than amplitude-dependent control of cGMP formation is possible. This suggests that it is the frequency of NO bursts and perhaps the frequency of Ca2+ oscillations in endothelial cells that may limit cGMP formation and regulate vascular tone. The proposed hypothesis suggests a new functional role for Ca2+ oscillations in endothelial cells. Further experimentation is needed to test whether and under what conditions in silico predictions occur in vivo.

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Nitric oxide and cGMP: mediators of pelvic nerve-stimulated erection in dogs

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1993.264.2.h419 ◽

1993 ◽

Vol 264 (2) ◽

pp. H419-H422 ◽

Cited By ~ 6

Author(s):

F. Trigo-Rocha ◽

W. J. Aronson ◽

M. Hohenfellner ◽

L. J. Ignarro ◽

J. Rajfer ◽

...

Keyword(s):

Nitric Oxide ◽

Smooth Muscle ◽

Muscle Relaxation ◽

Specific Inhibitor ◽

Phosphodiesterase Inhibitor ◽

Smooth Muscle Relaxation ◽

Pelvic Nerve ◽

Intracavernous Injection ◽

Penile Tumescence

We sought to determine whether the L-arginine-nitric oxide-guanosine 3',5'-cyclic monophosphate (cGMP) pathway, known to mediate neurostimulation-induced smooth muscle relaxation in penile tissue of rabbits and humans in vitro, is operative also in vivo. Adult male dogs (n = 9) were subjected to direct electrical stimulation of the pelvic nerves to induce penile tumescence. Intracavernous injection of the nitric oxide-releasing substance S-nitroso-N-acetylpenicillamine resulted in similar tumescence. Intracavernous injection of a specific inhibitor of nitric oxide synthesis, NG-nitro-L-arginine, blocked pelvic nerve-stimulated tumescence, and this was partially reversed by intracavernous injection of the nitric oxide precursor L-arginine. Furthermore, neurostimulated tumescence was inhibited by methylene blue, an inhibitor of cytosolic guanylate cyclase and enhanced by M&B 22948, a cGMP phosphodiesterase inhibitor. These in vivo findings support the hypothesis that cavernous smooth muscle relaxation and penile tumescence are mediated by nitric oxide and cGMP.

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Computational Modeling of Nitric Oxide Bioavailability in Hemolytic Anemias.

Blood ◽

10.1182/blood.v108.11.1209.1209 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1209-1209

Author(s):

Anne Jeffers ◽

Mark Gladwin ◽

Daniel Kim-Shapiro

Keyword(s):

Nitric Oxide ◽

Smooth Muscle ◽

Blood Cell ◽

Computational Modeling ◽

Red Blood Cell ◽

Muscle Relaxation ◽

Smooth Muscle Relaxation ◽

Rbc Membrane ◽

No Bioavailability

Abstract Intravascular hemoglobin (Hb) scavenges nitric oxide (NO), which decreases the availability of endothelial-derived NO, thereby reducing smooth muscle relaxation. Under normal conditions, there are various mechanisms that limit consumption of NO by Hb in vivo includinga physical barrier to NO diffusion across the red blood cell (RBC) membrane,an unstirred layer creating a concentration gradient in NO outside the RBC, andand a cell-free zone between the endothelium where NO is made and the location of the RBCs. However, in hemolytic conditions, these mechanisms can be compromised, leading to reduced levels of NO reaching the smooth muscle cells to cause vasodilation. Although it is generally accepted that cell-free Hb scavenges NO more effectively than Hb encapsulated in the red blood cell (RBC), some do not believe that the low concentrations of cell-free Hb that are present in hemolytic conditions, such as sickle cell disease, can impact NO bioavailability in the presence of the large amounts of RBC encapsulated Hb (about 10 mM in heme) present in vivo. We have performed computational modeling looking at the effects of cell-free Hb on NO bioavailability within blood vessels. We have found that concentrations of cell-free Hb as low as one micromolar significantly reduces the availability of NO. Thus, 0.01% hemolysis has a significant affect on steady state NO levels. Extravasation of cell-free Hb into the interstitial space of as low as one micromolar further reduces the bioavailability of NO. At low hematocrit values, cell-free Hb scavenging of NO was found to be more efficient than at high hematocrit values. We have also found that the effect of RBC membrane permeability diminishes at cell-free Hb concentrations of only four micromolar and above. These theoretical results support experimental evidence indicating that cell-free Hb contributes to the pathology of hemolytic diseases. Supported by NIH grant RG0489.

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