AJP - Cell Physiology, Vol 245, Issue 5 348-C356, Copyright © 1983 by American Physiological Society
Passive transport of K+ and Na+ in human red blood cells: sulfhydryl binding agents and furosemide
L. A. Wiater and P. B. Dunham
Passive transport pathways for K+ and Na+ were studied in fresh human red
blood cells (pretreated with ouabain) by measuring unidirectional influxes.
The effects of the sulfhydryl binding agents N-ethylmaleimide (NEM) and
p-chloromercuribenzene sulfonate (p-CMBS) and the loop diuretic furosemide
were studied. Influxes were measured at equimolar K+ and Na+ concentrations
(50 mM) with both ions present and also in K+-free or Na+-free media. Some
experiments were carried out in Cl--free media (with NO-3 as the
substitute). NEM stimulated K+ influx twofold; the stimulation required Cl-
but not Na+. NEM inhibited Na+ influx 20%. Furosemide inhibited both K+ and
Na+ influxes. All of furosemide-inhibitable Na+ influx required the
presence of K+. However 30% of furosemide-inhibitable K+ influx did not
require Na+. All of furosemide-inhibitable K+ influx required Cl-. The
ratio of Na+-dependent K+ influx to K+-dependent Na+ influx was 3:1. p-CMBS
stimulated both Na+ and K+ influxes. K+ influx in p-CMBS cells required
neither Na+ nor Cl-. Likewise p-CMBS-promoted Na+ influx did not require
K+. These various results are consistent with two Cl--dependent pathways
for K+ transport, one requiring Na+ [perhaps (Na + K + Cl) cotransport] and
one independent of Na+ [perhaps (K + Cl) cotransport]. The pathways
promoted by p-CMBS are probably independent of the apparent cotransport
systems.
