AJP - Cell Physiology, Vol 263, Issue 6 C1200-C1207, Copyright © 1992 by American Physiological Society
Anion channels for amino acids in MDCK cells
U. Banderali and G. Roy
Departement de Physiologie, Universite de Montreal, Quebec, Canada.
Large losses of amino acids by diffusion were previously observed in
Madin-Darby canine kidney (MDCK) cells during volume regulation. Also, an
outward rectifying anion channel was activated. Because this channel was
not selective among anions, it was suggested that it could be permeable to
amino acids. Its permeability to aspartate, glutamate, and taurine was
studied using the patch-clamp technique in the inside-out configuration.
Solutions containing 500 mM aspartate or glutamate were used on the
cytoplasmic side of excised patches to detect single-channel currents
carried by these anions. Permeability ratios were estimated in two
different ways: 1) from the shift in reversal potential of current-voltage
curves after anion replacement in the bath solution and 2) from comparisons
of amplitudes of single-channel currents carried by tested anions and
chloride, respectively. The values of aspartate-to-chloride and
glutamate-to-chloride permeability ratios obtained with both methods were
quite consistent and were of the order of 0.2 for both amino acids. Taurine
in solutions at physiological pH 7.3 is a zwitterionic molecule and bears
no net charge. To detect single-channel currents carried by taurine,
solutions containing 500 mM taurine at pH 8.2 were used in inside-out
experiments. Under these conditions 120 mM of negatively charged taurine
was present in the solutions bathing the cytoplasmic side of excised
patches. The permeability ratio estimated from the shift in reversal
potential was 0.75. These results showed that some of the organic compounds
released by cells during regulatory volume decrease could diffuse through
this outwardly rectifying anionic channel.
