Self-referencing voltage electrode technology was developed to detect steady extracellular currents by measuring the electrical field density (Jaffe & Nuccitelli, 1974). Kuhtreiber & Jaffe (1990) described a derivative of the original voltage-sensing electrode that was sensitive to specific ion species (SERIS electrodes). SERIS electrodes are based on standard neutral carrier ion-selective microelectrode technology, enabling changes in the activity of an ion to be measured potentiometrically (Smith, 1995). The SERIS electrode is stepped repeatedly at 0.3 Hz between two points, 10 µm apart. This makes a self-referencing voltage measurement that can be converted to a concentration for a selected ion at the extremes of the excursion (Smith, 1995). If there is a concentration gradient between these points, the measured concentration gradient can be related, by Fick’s Law, to a flux. Advantages over standard microelectrode techniques include non-invasiveness, sensitivity (under optimal conditions, nanovolt differences are resolvable) and the ability to detect electroneutral transport processes (Smith, 1995).
We have developed the SERIS electrode technique for use on pressurized arteries (Halpern pressure myography). It is difficult to apply conventional voltage-clamp techniques to pressurized arteries, and this has hindered identification of the ionic conductances activated during myogenic depolarization. Using SERIS electrodes, it is possible to detect changes in the extracellular concentration of the chosen ion close to the surface of a pressurized rat cerebral artery. This concentration gradient reflects the activity of ion channels, pumps and exchangers. Specifically we have measured both Ca2+– and Cl–-dependent fluxes from pressurized rat cerebral arteries during myogenic contraction. Arteries were removed from 200-250 g Wistar rats, killed by I.P. injection of sodium pentobarbitone (500 mg kg-1). Using this technique we have found evidence that increased Cl– and Ca2+ efflux from rat cerebral arteries is correlated with myogenic contraction (Langton & Smith, 1998; Doughty & Langton, 2001).
- Doughty, J.M. & Langton, P.D. (2001). J. Physiol. 534, 753-761. abstract
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