Measuring intracellular ion concentrations with multi-barrelled microelectrodes.

Ion-selective microelectrodes can be used to measure intracellular ion concentrations. The use of multi-barrelled electrodes enables the identification of the cellular compartment. For example, the inclusion of a pH-selective electrode enables the cytoplasm and vacuole to be distinguished. The ion-selective barrels of microelectrodes are filled with a sensor cocktail containing several different components. An ion-selective molecule, sensor or exchanger. Membrane solvent or plasticizer. Additives, e.g., lipophilic cation/anion. Membrane matrix to solidify the ion-selective membrane; essential for measurements in plant cells with a cell wall and turgor. For many ions, the ready-made membrane cocktail can be purchased, but the individual chemical components can be bought from suppliers and mixing the cocktail oneself is cheaper. For commercially available liquid membrane cocktails, the membrane matrix is not normally included. A matrix is needed if the microelectrodes are to be used in plants because cell turgor will displace a liquid membrane from the electrode tip, thereby changing or eliminating the sensitivity to the measuring ion. The matrix used is usually a high molecular weight poly(vinyl chloride), but can include other polymers, such as nitrocellulose for additional strength.