Measurements of the Cytoplasmic pH ofChara corallinausing Double-barrelled pH Micro-electrodes

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Abstract
A range of polymeric compounds was examined for their suitability as pressure-stabilizing agents in liquid membrane pH micro-electrodes for intracellular use in plant cells. Of the compounds tested, mixtures of liquid proton sensor and nitrocellulose were found to be superior to epoxy resins, polyvinylchloride and ethyl cellulose. The electrical resistance of silicone rubber mixtures was too high for micro-electrodes with tip diameters of 1.0 μm. Double-barrelled micro-electrodes containing nitrocellulose maintained excellent pH sensitivity for up to 1.0 impalements of charophyte cells. Measurements of cytoplasmic pH were made in both internodal and whorl cells of Chora corallina over a range of experimental conditions. The response of cytoplasmic pH to rapid changes in external pH or illumination occurred over several minutes. The advantages of the use of double-barrelled pH micro-electrodes over other methods of intracellular pH measurement such as the distribution of weak acids (DMO), 31P-NMR and single-barrelled micro-electrodes is discussed.

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