Physiologically Relevant Measurements of Nitric Oxide in Cardiovascular Research Using Electrochemical Microsensors

Abstract

Nitric oxide (NO) plays an important role in the regulation of blood flow. Pharmacological tools and a series of other techniques have been developed for studying the NO/L-arginine pathway, but it has proved difficult to make a quantitative link between effect and tissue NO concentration. NO microsensors have been applied with success for the measurement of NO in suspensions of mitochondria and cells, such as platelets and leukocytes, and in cell cultures, which together with other interventions or measurements are particularly useful for the examination of cell signalling related to the NO/L-arginine pathway. In isolated vascular segments, studies using the NO microsensor have defined the relationship between NO concentration and relaxation and revealed residual NO release in the presence of NO synthase inhibitors. Moreover, simultaneous measurements of NO concentration and vasorelaxation in isometric preparations have shown that agonist-induced relaxation is L-arginine dependent and NO release is reduced in hypertension. By placing NO microsensors in catheters, it is possible to measure NO in the living animal and man. This approach has been applied for the measurements of NO concentration in relation to increases in flow, erection, in conditions of hypoxia, and in endotoxemia. However, further methodological development of NO microsensors is necessary to avoid the influence of changes in temperature, pH and oxygen on the measurements.

Measurement of Nitric Oxide and Reactive Oxygen Species in the Vascular Wall

“…Only direct and real time measurements of NO levels in cells and tissues allow a conclusion on the exact NO concentration produced by a particular cell in response to a stimulus or in basal conditions. However, so far the results obtained by different investigations regarding to direct measurements of NO in living cells are disappointing since there is a huge variability in tissue NO concentrations determined by different groups using different direct electrochemical detectors [7,8]. …”

“…NO microsensors allow direct and real-time detection of NO generated in the nanomolar range both in vitro and in vivo [7][8][9][10]. The principle is that NO is oxidized at the surface of a working electrode, thus transferring one electron from the NO molecule to the anode generating current and nitrosonium cation (NO + ), which is finally converted to nitrite (NO 2 -).…”

“…The principle is that NO is oxidized at the surface of a working electrode, thus transferring one electron from the NO molecule to the anode generating current and nitrosonium cation (NO + ), which is finally converted to nitrite (NO 2 -). The first successful NO sensor was a miniature solid-state probe, based on the Clark electrode for the detection of oxygen, with a diameter of approximately 2 mm [7]. Malinski and co-workers [11] developed a much smaller microsensor based on a carbon fibre with a dual coating compromising polymerized metalloporphyrin and an outer layer of Nafion, which excluding access of nitrite.…”

“…No specific information is available concerning the nature of the membranes and their mechanisms of action, which is probably based on size and charge exclusion effects [12]. For further information about specific NO microsensors and how they are constructed please consult previous reviews [7,11,12]. NO microsensors have been applied for measurements in cell suspensions e.g.…”

“…[18][19][20][21][22]) (see ref. [7]). NO microsensors allow simultaneous measurements of NO concentration and vascular tone in isolated arteries [20][21][22][23].…”