Nitric oxide biological systems, direct

Brovkovych et al. [38] applied the electrochemical porphyrinic sensor technique for the direct measurement of NO concentrations in the single endothelial cell. It was found that NO concentration was the highest at the cell membrane (about 1 pmoll-1) and decreased exponentially with distance from the cell, becoming undetectable at the distance of 50 pm. Now we will consider the principal reactions of nitric oxide relevant to real biological systems. 

This contributes to the propensity of nitric oxide in dilute solutions to principally form nitrite rather than an equamolar amount of nitrite and nitrate as predicted by Reaction 22 (Ignarro, 1990 Ignarro et ai, 1993). In a biological system, nitrogen dioxide may also directly extract an electron from lipids or other compounds to form nitrite directly (Pryor and Lightsey, 1981). 

Because endothelial cells reside at the face of the valve in direct contact with blood flow, shear stress is a key regulator of endothelial cell function, communicating systemic changes in the body to the valvular tissue. Laminar shear stress, as observed at the ventricularis, regulates cell shape and microfilament structure as cells align in the direction of flow [60], correlated with synthesis of endothelial nitric-oxide synthase and production of nitric oxide, a potent vasodilator. Further discussion of the biological pathways altered by differential shear stresses is discussed later in the chapter. 

Since its identification as the endothelial derived relaxation factor (EDRF) there has been an explosive growth in the study NO (nitric oxide) in biological systems [38-42]. One of the difficulties associated with its study and determination is the fact that it has a very short lifetime. Thus, methodologies for the determination of NO have been largely indirect There is, however, a Rowing interest in the direct and in-vivo determination of NO. Because of their inherent sensitivity, electrochemical techniques are especially well suited for the development of analytical approaches for NO and the use of microelectrodes can allow, as was recently demonstrated, for in-vivo determinations [9c]. In addition, NO can be oxidized at about +0.80 V (vs SCE) at a platinum electrode (as well as at other electrode materials) although nitrite, ascorbate and other species can seriously interfere with the determination. In addition, in the case of in-vivo determinations, protein adsorption can also present difficidties. However, one can... 

---