Abstract:

Diffusion coefficient is an important parameter describing the diffusion process of a substance. However, the existing methods such as the membrane pool method, radioactive or fluorescent tracer method, and molecular dynamics simulation cannot be used to measure the ion diffusion coefficient in the biological system in real time. The ion-selective microelectrode has the advantages of rapid response, high selectivity, high sensitivity, high spatial resolution, and no pollution to the sample. Using the advantages of microelectrodes, this paper established the corresponding point source diffusion model by analyzing the ion concentration pulse signal formed by the rupture of protoplasts of single plant cells in culture medium, and derived the theoretical formula describing the ion concentration change with time. By fitting the experimentally measured pulse signal to obtain the diffusion coefficient of ions, a new method for in situ determination of ion diffusion coefficient by ion-selective microelectrode was established and applied to aloe cell protoplasts. When the ion diffusion coefficient is measured during the body rupture, the diffusion coefficients of Ca²⁺, Na⁺ and K⁺ are (6.51±0.12)×10^-6 cm²/s, (2.93±0.15)×10^-5 cm²/s and (3.03±0.35)×10^-5 cm²/s, respectively. The results show that the Ca²⁺, Na⁺, and K⁺ diffusion coefficients obtained are slightly higher than those reported values (in pure water). This phenomenon might be caused by the increase of the intracellular pressure of the protoplasts in the hypotonic fluid. The increased pressure might have accelerated the diffusion of ions when the cell ruptured. This method does not interfere with the biological system, and better solves the problem of in-situ real-time measurement of ion diffusion coefficient in biological systems.

Key words: ion, diffusion coefficient, microelectrode, in situ, protoplast