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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 microm. Calibration using various concentrations of NO (0.1-1.0 microM) showed that the electrode has good linearity (r = 0.99) and its detection limit is 0.075 microM (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 NG-nitro-L-arginine methyl ester (L-NAME), a putative NO synthase inhibitor, NO release (peak NO concentration) from RAECs was significantly less than that in the absence of L-NAME (0.18 +/- 0.04 microM vs 0.47 +/- 0.13; P < 0.01). After removal of L-NAME, NO release partially recovered (0.39 +/- 0.10 microM). In conclusion, the microcoaxial electrode was successfully applied to direct and continuous NO measurement in biological systems.

A new nitric oxide (NO) selective electrode was developed. The tip diameter of the NO electrode is less than 10 μm. A working and a reference electrodes are located coaxially at the tip of the NO electrode. A stable NO donor SNAP (S-nitroso-N-acetyl-DL-penicillamine) and a putative NO scavenger hemoglobin (Hb) was used to examine the response of the electrode. Considering the instantaneous concentration of NO secretion previously reported in biological systems, 0.1, 1 μM NO solution was used to calibrate the electrode. From the result of the test of the electrode with SNAP and Hb, we confirmed this microcoaxial NO electrode can detect NO released from SNAP directly and continuously. From the result of calibration of the electrode, good linearity was examined in sub-molar concentration range. It is expected to detect local NO concentration in biological systems with a high space resolution.