AJP - Renal Physiology, Vol 258, Issue 2 438-F443, Copyright © 1990 by American Physiological Society
Synthesis and characterization of a new fluorescent probe for measuring potassium
K. Golchini, M. Mackovic-Basic, S. A. Gharib, D. Masilamani, M. E. Lucas and I. Kurtz
Division of Nephrology, University of California, School of Medicine, Los Angeles 90024.
A new fluorescent probe, 6,7-(4-methyl)coumaro-[2.2.2] cryptand, has been
developed for measuring K+. This compound was made by fusing [2.2.2]
cryptand with 4-methylcoumarin through 2 ethoxy bridges at the 6 and 7
positions. The probe has a fluorescent excitation peak at 340 nm and an
emission peak at 420 nm. In aqueous solutions, increasing the K+
concentration from 0 to 10 mM causes the fluorescence intensity to increase
by 143%. The dissociation constant (Kd) for K+ in aqueous solutions is 1.9
mM. In 100% methanol, the Kd for K+ decreases to 0.012 mM, making it
possible to measure K+ concentrations in the micromolar range. Na+,
tetramethylammonium, NH4+, Ca2+, and Mg2+ have a minimal affect on the
fluorescence of the probe in the absence of K+. The coefficient of
variation for the measurement of K+ by use of this new dye is less than 1%.
In this report, the synthetic procedure is described and the spectral
properties of the probe are characterized. Experiments are described
demonstrating the use of this probe 1) in measuring K+ in aqueous solutions
from 0 to 10 mM and in a microfluorometric assay to measure K+ from 0.0005
to 0.003 mM and 2) in monitoring K+ transport in rabbit proximal tubule
brush-border membrane vesicles.
