Low impedance coaxial K+ selective microelectrodes

Abstract

A procedure for preparing coaxial K+ selective microelectrodes with a low longitudinal resistance (Re) of the liquid ion exchanger selective barrel is described. The low resistance was attained by inserting another microelectrode filled with 0.5 mol . 1-1 KCl into the ion-exchanger column (Corning 477317). The lower longitudinal resistance decreases the noise level and consequently increases the resolving power five times. This modification makes it possible to measure small and rapid K+ concentration changes.

Fabrication and Use of High-Speed, Concentric H+- and Ca2+-Selective Microelectrodes Suitable for In Vitro Extracellular Recording

“…In this report, we used the concentric concept of Orme and borrowed aspects of construction from Ujec et al (1979Ujec et al ( , 1981, to fabricate concentric ISMs selective for H ϩ and Ca 2ϩ . The present design benefited from several key modifications.…”

“…In this conception, the central pipette would serve to reduce the longitudinal resistance of the column and thereby decrease the electrical time constant. Ujec and colleagues first tested this method for the construction of K ϩ -, Cl Ϫ -, and Ca 2ϩ -selective microelectrodes (Ujec et al 1979(Ujec et al , 1981. Later, Pumain et al (1983) used this concentric modification to speed the response of neutral carrier, Ca 2ϩ -selective microelectrodes and, in a study of cat cortex, discerned rapid, in vivo decreases in extracellular Ca 2ϩ activity ([Ca 2ϩ ] e ) during epileptic discharges.…”

“…This is not surprising given the complexity of design. The assemblies described by Ujec et al (1979Ujec et al ( , 1981 used a triplebarreled configuration that consisted of a large-diameter ion barrel, a smaller-diameter reference barrel, and a small, independent concentric pipette threaded within the ion-selective side. This technique made use of specially fused capillaries of different-diameter glass tubing.…”

Calcium-Sensitive Mini- and Microelectrodes

“…The response time can also be improved by using Ca 2+ -selective microelectrodes with a concentric inner micropipette that reduces the longitudinal resistance of the Ca 2+ -selective resin and thereby decreases the electrical time constant (Ujec et al 1979;Fedirko et al 2006). For intracellular measurements, the relatively slow response time and the physical size of Ca 2+ -selective microelectrodes make them less advantageous for dynamic [Ca 2+ ] i measurements, compared with fluorescent and luminescent Ca 2+ indicators.…”

Ion-selective electrodes

“…Reducing noise problems associated with the use of conventional micropipet-based microelectrodes has been the focus of several research efforts. Ujec et al (42e,43e) proposed low impedance double-barrel micro ISEs for potassium and calcium by introducing, coaxially, a thin micropipet into the ISE barrel. This effectively reduces the longitudinal distance between the sample solution and the internal electrolyte (i.e., effectively a thinner ISE membrane at the electrode tip) yielding reduced resistance and less noise.…”