Antimony microelectrode

As renal physiologists developed the technique of micropuncture, investigators sought an electrode to measure pH which did not allow carbon dioxide to equilibrate with the bicarbonate in vitro as happens with the quinhydrone electrode. An alternative was the ultramicroglass electrode (6), but the technical difficulties in its fabrication (1) stopped many potential users. In 1968, Malnic and Vieira (9) introduced the micro antimony electrode into micropuncture research and have used it extensively since then (5). Because of increasing usage of antimony microelectrodes, a survey of some hitherto undescribed difficulties we encountered in its use should be most helpful to other investigators. 

It would appear that antimony electrodes can be used reliably in experiments on proximal renal tubules, where there is little change in the phosphate buffer concentration and probably no change in ionic strength, providing that the phosphate buffers and ionic strength of the standards match the unknown fluid. Questionable data should be expected with antimony microelectrodes in distal tubules, collecting ducts and in final urine, where ionic composition and buffer capacity vary widely. 

In summary, when using antimony microelectrodes the standards should have the same phosphate concentration and total ionic strength as the unknown and all measurements should be made in drops of equal size. All readings are time dependent, and in small drops, the reading should be taken after a suitable time interval, usually 1-2 minutes. 

In spite of the variations evidently inherent in the antimony microelectrode, it is still possible to use the antimony microelectrodes reproducibly as is shown in Table 2. In the table the actual concentrations of acid are compared with the analyzed titratable acidity" of 5 nl samples, and the agreement is quite close. The coefficient of variation is between 5-107o which is as good as most methods used in micropuncture work. 

Vieira, F.L. and Malnic, G. Hydrogen Ion Secretion by Rat Renal Cortical Tubules as Studied by an Antimony Microelectrode, Amer. J. Physiol. 214 710-718 (1968). 

KINETIC ANALYSIS OF RENAL TUBULAR ACIDIFICATION BY ANTIMONY MICROELECTRODES... 

The use of antimony microelectrodes which are metal/metal oxide electrodes, is shown in Fig. la. They consist of antimony-filled glass capillaries, which are drawn out in order to obtain a fine bevelled tip, which is pH-sensitive and can be introduced into the tubular lumen. These electrodes have also been used to measure titratable acidity and ammonia in an in vitro" system, according to Solomon et al (16) and Karlmark (6). In this paper we will restrict ourselves to the discussion of some aspects of tubular acidification which can be studied due to the rapid response of the antimony electrode system to pH changes, permitting the kinetic study of the tubular acidification mechanisms. 

Fig. 1. Schematic diagram of the use of antimony microelectrode for tubular pH measurements, a, pH determination during free flow. b, continuous recording of tubular pH during stopped flow microperfusion.

Fig. 5. Schematic drawing of Voltage clamp" experiments on renal cortical tubules. Sb, antimony microelectrode NaCl, current passing microelectrode A, amplifier V, voltage recording as obtained by Sb microelectrode, representing superposition of voltage and pH changes I, current recording.

The foregoing discussion shows the potentiality of the use of antimony microelectrodes for kinetic studies on renal tubular acidification. It must be stressed, however, that the interpretation of the obtained results is still only tentative, and considerable effort will have to be made to distinguish between some of the presented alternatives, and to overcome some of the inherent draw-backs of the method. However, we believe that this method is able to bring considerable progress to the understanding of the mechanism of renal tubular acidification. 

Absolute Accuracy of Measurement, 13-20 Accuracy of K Microelectrode, 77-85 Acetazolamide, 95-98, 100 Acetylcholine Effects, 58, 61 Acidification, Renal Tubular, 89 Antimony Microelectrodes, 43, 89 Aplysia Neurons, 57 Artificial Beta Cell, 189 Artificial Pancreas, 189... 

It can be seen from the reactions (10.12) and (10.13) that the oxygen released from cuprous oxide should react with hydronium ions increasing the surface pH. This effect can be confirmed experimentally by probing with pH-sensitive microelectrodes. One of them, Sb SbjOj microprobe, was used in the following experiments. This antimony microelectrode (AME) is reversible with respect to H+ ions and its equilibrium potential is determined unambiguously by the solution pH (see Section 3.4.1). The design ofthe equipment permitted the position of the AME tip to be controlled with an accuracy of 10 pm. The distance of closest approach ofthe AME to the electrode surface. Ax, was arbitrarily taken as zero. 

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