AJP - Cell Physiology, Vol 256, Issue 1 C81-C88, Copyright © 1989 by American Physiological Society
Volume-sensitive, Cl-dependent K transport in resealed human erythrocyte ghosts
W. C. O'Neill
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30303.
Potassium influx and efflux in Cl and NO3 media were measured in resealed
ghosts prepared from human red cells. Cl-dependent K influx was three times
that in intact cells and, as in intact cells, was partially supported by Br
but not by thiocyanate (SCN). In other properties, this flux differed from
that in intact cells: substitution of N-methylglucamine for Na did not
decrease but rather increased Cl-dependent K influx, the affinity for
external K was reduced, with a Km of 21.3 +/- 12.5 mM, and inhibition by
furosemide and bumetanide was incomplete. Furosemide at 1 mM inhibited
Cl-dependent influx by 26 and 51% at 4 and 20 mM K, respectively.
Bumetanide inhibited Cl-dependent K influx by 0 and 55% at concentrations
of 10 microM and 1 mM, respectively, in 4 mM K, with no further inhibition
at 20 mM K. Neither the magnitude nor the properties of the flux were
altered by preparing ghosts in the presence of 1,4-dithiothreitol,
indicating that sulfhydryl oxidation was not responsible for the altered
flux in ghosts. Treatment with N-ethylmaleimide (NEM) either before or
after ghost preparation did not increase Cl-dependent K influx. However,
Cl-dependent influx in ghosts could be augmented by increasing ghost volume
or ATP content. Resealed human erythrocyte ghosts thus exhibit a volume-
and ATP-sensitive, Cl-dependent K flux that differs substantially from the
putative Na-K-Cl cotransport in intact cells in that it is independent of
Na, is relatively resistant to furosemide and bumetanide, and has a low
affinity for K.(ABSTRACT TRUNCATED AT 250 WORDS)
