Microcoaxial electrode for in vivo nitric oxide measurement

Nitric oxide (NO) is a gaseous mediator involved in various physiological p henomena, such as vasorelaxation and neurotransmission. Investigation of lo cal cellular responses of NO production in vivo and in vitro requires a mea surement method with a high spatial resolution. For selective NO measuremen t, we therefore developed a microcoaxial electrode whose tip diameter is le ss than 10 mu m. Calibration using various concentrations of NO (0.1-1.0 mu M) showed that the electrode has good linearity (r = 0.99) and its detecti on limit is 0.075 mu M (S/N = 3). We verified the applicability of this ele ctrode to in vivo and in vitro local measurement NO released from bovine ao rtic cultured endothelial cells (BAECs) stimulated by acetylcholine (ACh). After the addition of ACh, a transient increase in NO concentration was det ected by the electrode. In the presence of N-G-nitro-L-arginine methyl este r (L-NAME), a putative NO synthase inhibitor, NO release (peak NO concentra tion) from BAECs was significantly less than that in the absence of L-NAME (0.18 +/- 0.04 mu M vs 0.47 +/- 0.13; P < 0.01). After removal of L-NAME, N O release partially recovered (0.39 +/- 0.10 mu M). In conclusion, the micr ocoaxial electrode was successfully applied to direct and continuous NO mea surement in biological systems.