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GLASS MICROCAPILLARY ELECTRODES 



USED FOR MEASURING POTENTIAL 



IN LIVING TISSUES 



D. W. KENNARD 



MICROCAPILLARY ELECTRODES FOR INTRACELLULAR 

 RECORDING BY TRANSVERSE MEMBRANE PUNCTURE 



Electrical potentials and currents may be detected about most biological 

 tissues. Those of greatest physiological interest are due to work performed 

 by living tissues in separating the electrically charged ionic particles. The 

 electrical energy required to do this work can be stored in tissues such as 

 nerve and muscle which form concentration cells, from which it can be 

 liberated without the aid of metabolic activity. Tissues may be regarded 

 as batteries which pass current through an external circuit composed of 

 the saline medium of the living organism. 



To study the electrical activity of individual cells an electrode can be 

 introduced into the interior and the potential difference (P.D.) across the 

 cell walls determined. If the cell is large enough the electrode can be 

 introduced through a cut end, as was done by Hodgkin and Huxley^ and 

 Curtis and Cole^, using the giant nerve fibre of the squid. They found that 

 by introducing a capillary electrode of 60 jjl diameter for a distance of 

 2-3 cm undamaged portions of the cell could be studied. 



For most cells the cell wall has to be punctured by the electrode itself, 

 which is made as small as possible to minimize damage. The first successful 

 punctures of this type were made by Ling and Gerard^ using electrodes 

 of about 0-5 [I diameter in the striated muscle fibres of the frog. Electrodes 

 for intracellular work are required to record both steady potential levels 

 and rapid fluctuations of voltage. The simplest method of establishing 

 connection between a tissue and a measuring device is to use a suitable 

 metallic conductor. Such a connection, though useful for recording fluctua- 

 tions of voltage, introduce difficulties in measuring steady levels. When any 

 metal is immersed in a saline medium a P.D. is established between it and 

 the fluid; the actual values depend on the nature of the metal and the fluid. 

 For example the tungsten electrode potential depends on the concentration 

 of hydrogen ions present (Britton"*) and has been used to measure intra- 

 cellular pH (CaldwelF). The potential of a silver electrode depends on the 

 halide ions present and has been used to estimate chloride ion. 



During the course of an experiment, however, the composition of tissue 

 fluids may vary, causing potential changes. To ensure stable electrode 

 voltages the electrode environment must be constant, and this can be achieved 



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