Online electrochemical measurements of Ca2+ and Mg2+ in rat brain based on divalent cation enhancement toward electrocatalytic NADH oxidation.

This study describes a novel electrochemical approach to effective online monitoring of electroinactive Ca(2+) and Mg(2+) in the rat brain based on the current enhancement of divalent cations toward electrocatalytic oxidation of NADH. Cyclic voltammetry for NADH oxidation at the electrodes modified with the polymerized film of toluidine blue O (TBO) reveals that the current of such an electrocatalytic oxidation process is remarkably enhanced by divalent cations such as Ca(2+) and Mg(2+). The current enhancement is thus used to constitute an electrochemical method for the measurements of Ca(2+) and Mg(2+) in a continuous-flow system with the polyTBO-modified electrode as the detector. Upon being integrated with in vivo microdialysis, the electrochemical method is successfully applied in investigating on cerebral Ca(2+) and Mg(2+) of living animals in two aspects: (1) online simultaneous measurements of the basal levels of Ca(2+) and Mg(2+) in the brain of the freely moving rats by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca(2+) to differentiate the net current responses selectively for Ca(2+) and Mg(2+); and (2) online continuous monitoring of the cerebral Mg(2+) following the global ischemia by using Ca(2+)-masking agent (i.e., EGTA) to completely eliminate the interference from Ca(2+). Compared with the existing methods for the measurements of cerebral Ca(2+) and Mg(2+), the method demonstrated here is advantageous in terms of its simplicity both in instrumentation and in the experimental procedures and near real-time nature, and is thus highly anticipated to find wide applications in understanding of chemical events involved in some physiological and pathological processes.