Application of implanted electrodes in medical practice for treatment (for example neuro or cardio stimulation) and diagnostics (for example monitoring of intracranial pressure) requires rigorous selection of materials and regimes of electrostimulation to avoid a traumatic effect on blood and other tissues during prolonged contact electrode with organism. Efficiency of electrodes depends on various factors, therefore knowledge of the mechanism of interactions in the systems [electrode]/[body tissue], in particular in the system [electrode]/[blood], is very important.

Earlier it was obtained by polarization and coulometric measurements in the system [electrode]/[erythrocytes suspension] that electrochemical processes of oxidation and reduction of blood cells on the surface of a platinum electrode occurred [1], that is, electron transport between blood cells and an electrode was proved. Probably electrochemical transformations in the systems [electrode]/[body tissue] (in this case [electrode]/[blood]) can undergo functional groups of protein complexes located on the surface of the blood cell membranes.

In order to obtain quantitative criteria for the detected electrochemical activity of blood cells and to determine the effect of electrode material on the course of electrochemical processes, it was decided to investigate the electrochemical behavior of erythrocytes on a glassy carbon electrode and obtain data on the number of electrons necessary for electrochemical processes involving blood cells.

Polarization measurements were carried out in a three-electrode cell with separated cathode and anode chambers in the erythrocytes suspension in a deoxygenated aqueous solution of 0.15 M NaCl. The working electrode was a rotating disk electrode (RDE) made of glassy carbon (GC) of 3 mm diameter; rotation speed was from 500 rpm to 2000 rpm. The erythrocytes suspension was obtained from whole blood by centrifugation in a centrifuge CR 3.12 (Jouan, France) at 1500g. The concentration of cells in the suspension for the study was 8·10¹⁰ cells/L.

It was found electroreduction wave on GCE in erythrocytes suspension like platinum electrode (Fig.1 (a)). Thus, the transfer of electrons from the surface of the GCE to the erythrocyte membrane was proved. However half-wave potential E_1/2=-770 mV unlike E_1/2 = -420 mV on platinum electrode. Moreover, the process of electrooxidation of erythrocytes was observed too on GCE like platinum.

Cathode polarization curves in the erythrocytes suspension obtained at different rotational speeds of the GCE showed that the value of the limiting current of the electroreduction process linearly depends on the square root of the rotational speed of electrode (Fig.1 (b)). Thus according to the Levich theory of convective diffusion the process of electroreduction of the erythrocytes suspension is limited by the diffusion of cells to the electrode. Unfortunately, it was not possible to determine experimentally the concentration of electrochemically active groups on the membrane surface of erythrocyte. Therefore the calculations were performed on the assumption that only the disulfide groups of main sialoglycoprotein of the erythrocyte membrane (glycophorin A) can undergo electroreduction.

In total, according to the data [2], on the erythrocyte membrane there are ~ 5·10⁵ molecules of glycophorin A. Taking into account the content of erythrocytes in the suspension, the concentration of glycophorin A on the surface of the cell membrane was C₀ = 6.64·10^-11 mol/cm³. The diffusion coefficient of erythrocytes is D = 1.6·10^-9 cm²/s [3], and the kinematic viscosity of the blood is ν = 0.04 cm²/s [4]. Substituting these values into Levich's equation, it was obtained that the value of the number of electrons for the electroreduction of erythrocytes was 3.4 10⁶ electrons per cell.

The obtained high magnitude of number of electrons is probably associated with a large number of functional groups on the erythrocyte membrane. Analysis of literature data has shown that the number of electrons for the process of oxidation or reduction of protein molecules also has high values. For example, for the process of reduction of albumin on a dropping mercury electrode, the number of electrons is 10.5 for the reduction of disulfide groups in the protein composition, and for the process of adsorption of the hemoglobin molecule on activated carbon the number of effective electrons is about 1000 [5].

Thus the transport of electrons in the system [glassy carbon]/[erythrocyte] was detected and quantitatively characterized.

Reference

1. Tsivadze A.Y., Khubutiya M.Sh., Goroncharovskaya I.V. [et al.] // Mendeleev Commun. 2017; 27(2): 183-5.
2. Steck T.L. // J. Cell. Biol. 1974; 62(1): 1-19.
3. Fritz O.G. // Biophys. J. 1984; 46(2): 219-27.
4. Biomedical Engineering Fundamentals / J.D. Bronzino, D.R. Peterson (Eds.). – Boca Raton: CRC Press, 2014. – 1180 p.
5. Khubutiya M.Sh., Grafov B.M., Goldin M.M.[et al.] // J. Solid State Electrochem. 2012; V. 16(11): 3505-14.