ULTRAMICROELECTRODES FOR MEMBRANE RESEARCH

This article describes the construction, testing, calibration and appl ication of ion-selective double-barrelled microelectrodes based on neu tral carrier or ion-exchanger liquid membranes. At present the use of ion-selective microelectrodes is the only method available for the dir ect and continuous measurement of ion activities in the intra-and extr acellular spaces, on membrane surfaces, and even in subcellular organe lles of a variety of intact cells. Intracellular ion activities in ide ntified neurones of the central nervous system of the leech (Hirudo me dicinalis L.) have been measured with K+-, Na+-, H+-, Mg2+- and Ca2+-s elective double-barrelled microelectrodes under various experimental c onditions, such as changes in ion composition of the external medium, application of neurotransmitters and exposure to drugs. This approach has provided significant information about electrochemical potentials of ions, properties of receptor-coupled ion channels, and membrane tra nsport related to ion activities in this nervous system. (C) 1997 Publ ished by Elsevier Science Ltd.