AJP - Heart and Circulatory Physiology, Vol 258, Issue 4 1224-H1231, Copyright © 1990 by American Physiological Society

ARTICLES

Fabrication, evaluation, and use of extracellular K+ and H+ ion-selective electrodes

T. A. Johnson, C. L. Engle, R. P. Kusy, S. B. Knisley, C. A. Graebner and L. S. Gettes
Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27599-7075.

Ion-selective mini-electrodes have been widely employed to measure extracellular K+ and H+ during myocardial ischemia. However, the recent availability of this technology has not been accompanied by uniform fabrication, amplification, and calibration standards. In their fabrication, the chloride tips of Teflon-coated silver wires should be covered with a cellulose acetate-titanium dioxide sponge followed by a polyvinyl chloride (PVC)-valinomycin (K+) or PVC-tridodecylamine (H+) ion-selective membrane. Critical analysis of the nonworking electrodes using scanning electron micrographs has revealed membrane holes, membrane and sponge contamination, Teflon plaque, poor membrane-sponge-Teflon adhesion, and improperly applied or torn membrane. We have also found that signal amplification must have variable-gain filtration (0-1 Hz) with 0.5-pA input offset current and 10(12)-omega input resistance. Furthermore, in vitro calibration in 3 and 10 mM KCl (K+) or pH 8 and 6 buffer (H+) should produce a Nernstian slope +/- 5 or 10%, respectively, at 26 degrees C with a response time less than or equal to 50 ms, resistance greater than or equal to 10(12) omega, and drifts less than or equal to 1 mV/h. In vivo performance and calibration criteria (delineated for K+ only) include 1) transient response to bolus injections of KCl (0.12 mM/kg body wt) yielding peak amplitude changes of 2.5-3.0 mM, response times less than or equal to 10 s, and washout time constants less than or equal to 3 min, and 2) in vivo calibration to artificial independently confirmed systemic [K+] producing a Nernstian slope +/- 15% at 38 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

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