Reference Microelectrodes

The Ag/AgCl micropipette reference electrodes usually employed in physiological measurements of cell membrane potentials can be used as reference electrodes for intracellular ion activity measurements as well. The salt bridge electrolyte must be chosen with care so that the intracellular measured ion concentration is not influenced. 

There are two possibilities concerning the positioning of the merely 1 jjl diameter reference electrode tip in the cell structure  

---

Figure 1 Schematic diagrams illustrating the patch-clamp technique. (A) Overall setup for isolating single ionic channels in an intact patch of cell membrane. P = patch pipet R = reference microelectrode I = intracellular microelectrode Vp = applied patch potential Em = membrane potential Vm = Em — Vp = potential across the patch A = patch-clamp amplifier. (From Ref. 90.) (B) Five different recording configurations, and procedures used to establish them, (i) Cell attached or intact patch (ii) open cell attached patch (iii) whole cell recording (iv) excised outside-out patch (v) excised inside-out patch. Key i = inside of the cell o = outside of the cell. (Adapted from Ref. 283.)...

Ag/AgCl reference microelectrodes, from Microelectrodes, Inc. (Bedford, USA). 

Recording Schematic for K Selective Microelectrode, 131 Reference, microelectrode, 13, 77, 111, 129, 147 Relationship of Surface Skeletal Muscle pH to Blood pH, 181 Reliability of Data, 6, 13... 

In case of potentiometric measurements with microelectrode arrays, complete micro-reference electrodes have been suggested. The term complete microreference electrode is used here for such reference electrodes that consist of the same parts as conventional macroelectrodes. Their operating principle is essentially identical to that of the latter. Major difference is the size. Needle-type reference electrodes are frequently used for miniaturisation. The Ag/AgCl system (or a similar one) is hosted in a capillary with dimensions in the millimetre range. The capillary is thinned at one end, and the orifice houses the liquid junction. Commercially available complete reference microelectrodes have capillaries with an outer diameter of 1-2 mm at the end. The liquid junction is realised by a ceramic frit or a fibre. A real micro-reference electrode has been described by Kitade and coworkers [26]. They used a commercially available Femtotip capillary tube as the electrode body. Such tips have a capillary with an outer diameter of 1 pm and are usually used for microinjection into adherent and suspension cells. The tip is filled with a KCl agar gel to realise the liquid junction. The bare part of the silver wire has to be covered with a polystyrene membrane to avoid any additional potential between the inner electrolyte solution and the bare silver wire. 

---