title: Fabrication, evaluation, and use of extracellular K+ and H+ ion-selective electrodes.
abstract: 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)
authors.affiliation: Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27599-7075.
authors.forename: T A
authors.initials: TA
authors.lastname: Johnson
authors.forename: C L
authors.initials: CL
authors.lastname: Engle
authors.forename: R P
authors.initials: RP
authors.lastname: Kusy
authors.forename: S B
authors.initials: SB
authors.lastname: Knisley
authors.forename: C A
authors.initials: CA
authors.lastname: Graebner
authors.forename: L S
authors.initials: LS
authors.lastname: Gettes
mesh_terms: D000818:Animals; D002138:Calibration; D003625:Data Collection; D004559:Electric Wiring; D004563:Electrochemistry / Q000295:instrumentation*; D004566:Electrodes; D004867:Equipment Design; D004868:Equipment Failure; D005069:Evaluation Studies as Topic; D005110:Extracellular Space / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*
chemical_list: D006859:Hydrogen; D011188:Potassium