Intracellular smooth muscle [Ca2+] in acetylcholine and nitric oxide-mediated relaxation of human small arteries

Systems biology of HBOC-induced vasoconstriction

Vasoconstriction is a major adverse effect of HBOCs. The use of a single drug for attenuating HBOC-induced vasoconstriction has been tried with limited success. Since HBOC causes disruptions at multiple levels of organization in the vascular system, a systems approach is helpful to explore avenues to counteract the effects of HBOC at multiple levels by targeting multiple sites in the system. A multi-target approach is especially appropriate for HBOC-induced vasoconstriction, because HBOC disrupts the cascade of amplification by NO-cGMP signaling and protein phosphorylation, ultimately resulting in vasoconstriction. Targeting multiple steps in the cascade may alter the overall gain of amplification, thereby limiting the propagation of disruptive effects through the cascade. As a result, targeting multiple sites may accomplish a relatively high overall efficacy at submaximal drug doses. Identifying targets and doses for developing a multi-target combination HBOC regimen for oxygen therapeutics requires a detailed understanding of the systems biology and phenotypic heterogeneity of the vascular system at multiple layers of organization, which can be accomplished by successive iterations between experimental studies and mathematical modeling at multiple levels of vascular systems and organ systems. Towards this goal, this article addresses the following topics: a) NO-scavenging by HBOC, b) HBOC autoxidation-induced reactive oxygen species generation and endothelial barrier dysfunction, c) NO- cGMP signaling in vascular smooth muscle cells, d) NO and cGMP-dependent regulation of contractile filaments in vascular smooth muscle cells, e) phenotypic heterogeneity of vascular systems, f) systems biology as an approach to developing a multi-target HBOC regimen.

Vasodilator efficacy of nitric oxide depends on mechanisms of intracellular calcium mobilization in mouse aortic smooth muscle cells

BACKGROUND AND PURPOSE

Reduction of intracellular calcium ([Ca(2+)](i)) in smooth muscle cells (SMCs) is an important mechanism by which nitric oxide (NO) dilates blood vessels. We investigated whether modes of Ca(2+) mobilization during SMC contraction influenced NO efficacy.

EXPERIMENTAL APPROACH

Isometric contractions by depolarization (high potassium, K(+)) or alpha-adrenoceptor stimulation (phenylephrine), and relaxations by acetylcholine chloride (ACh), diethylamine NONOate (DEANO) and glyceryl trinitrate (GTN) and SMC [Ca(2+)](i) (Fura-2) were measured in aortic segments from C57Bl6 mice.

KEY RESULTS

Phenylephrine-constricted segments were more sensitive to endothelium-derived (ACh) or exogenous (DEANO, GTN) NO than segments contracted by high K(+) solutions. The greater sensitivity of phenylephrine-stimulated segments was independent of the amount of pre-contraction, the source of NO or the resting potential of SMCs. It coincided with a significant decrease of [Ca(2+)](i), which was suppressed by sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA) inhibition, but not by soluble guanylyl cylase (sGC) inhibition. Relaxation of K(+)-stimulated segments did not parallel a decline of [Ca(2+)](i). However, stimulation (BAY K8644) of L-type Ca(2+) influx diminished, while inhibition (nifedipine, 1-100 nM) augmented the relaxing capacity of NO.

CONCLUSIONS AND IMPLICATIONS

In mouse aorta, NO induced relaxation via two pathways. One mechanism involved a non-cGMP-dependent stimulation of SERCA, causing Ca(2+) re-uptake into the SR and was prominent when intracellular Ca(2+) was mobilized. The other involved sGC-stimulated cGMP formation, causing relaxation without changing [Ca(2+)](i), presumably by desensitizing the contractile apparatus. This pathway seems related to L-type Ca(2+) influx, and L-type Ca(2+) channel blockers increase the vasodilator efficacy of NO.

Nitric oxide selective electrodes

Since nitric oxide (NO) was identified as the endothelial-derived relaxing factor in the late 1980s, many approaches have attempted to provide an adequate means for measuring physiological levels of NO. Although several techniques have been successful in achieving this aim, the electrochemical method has proved the only technique that can reliably measure physiological levels of NO in vitro, in vivo, and in real time. We describe here the development of electrochemical sensors for NO, including the fabrication of sensors, the detection principle, calibration, detection limits, selectivity, and response time. Furthermore, we look at the many experimental applications where NO selective electrodes have been successfully used.