Microcoaxial electrode for in vivo nitric oxide measurement

Nitric oxide (NO) is a gaseous mediator involved in various physiological phenomena, such as vasorelaxation and neurotransmission. Investigation of local cellular responses of NO production in vivo and in vitro requires a measurement method with a high spatial resolution. For selective NO measurement, we therefore developed a microcoaxial electrode whose tip diameter is less than 10 μm. Calibration using various concentrations of NO (0.1-1.0 μM) showed that the electrode has good linearity (r = 0.99) and its detection limit is 0.075 μM (S/N = 3). We verified the applicability of this electrode to in vivo and in vitro local measurement NO released from bovine aortic cultured endothelial cells (BAECs) stimulated by acetylcholine (ACh). After the addition of ACh, a transient increase in NO concentration was detected by the electrode. In the presence of N(G)-nitro-L-arginine methyl ester (L-NAME), a putative NO synthase inhibitor, NO release (peak NO concentration) from BAECs was significantly less than that in the absence of L-NAME (0.18 ± 0.04 μMvs 0.47 ± 0.13; P < 0.01). After removal of L-NAME, NO release partially recovered (0.39 ± 0.10 μM). In conclusion, the microcoaxial electrode was successfully applied to direct and continuous NO measurement in biological systems.