AJP - Cell Physiology, Vol 255, Issue 3 C408-C412, Copyright © 1988 by American Physiological Society
Double-barreled K+-selective microelectrodes based on dibenzo-18-crown-6
J. L. Mooney, V. Lyall, M. Acevedo and W. M. Armstrong
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46223.
Liquid ion-exchanger microelectrodes based on Corning code 477317 K+
exchanger are known to be much more sensitive to quaternary ammonium ions
than to K+. In the presence of such cations, the capability of measuring K+
activities with Corning microelectrodes may be seriously impaired. We have
developed a neutral carrier K+-selective microelectrode based on the crown
ether dibenzo-18-crown-6. The crown ether cocktail contained (wt/wt) 2.3%
dibenzo-18-crown-6, 0.8% Na-tetraphenylborate, 30.1%
2-nitrophenylocylether, and 66.8% O-nitrotoluene. Double-barreled crown
ether and Corning microelectrodes were calibrated in KCl solutions with or
without choline, acetylcholine, tetramethylammonium, imidazole, Na+,
tris(hydroxymethyl)aminomethane (Tris), and N-methyl-D-glucamine. Both
kinds of microelectrodes showed similar K+ over Na+, Tris, and
N-methyl-D-glucamine selectivities. However, crown ether microelectrodes
had immensely greater selectivities of K+ over quaternary ammonium ions and
imidazole than Corning microelectrodes. Selectivity factors, defined as log
K(ij)K, of crown ether microelectrodes with respect to K+ for
tetramethylammonium, choline, acetylcholine, and imidazole were -1.92 +/-
0.13, -2.97 +/- 0.03, -1.75 +/- 0.15, and -1.30 +/- 0.20, respectively.
Intracellular K+ activities measured in the same Necturus gallbladders with
both kinds of microelectrodes did not differ significantly.
