AJP - Cell Physiology, Vol 249, Issue 5 490-C496, Copyright © 1985 by American Physiological Society
Kinetics of Cl-dependent K influx in human erythrocytes with and without external Na: effect of NEM
D. Kaji and T. Kahn
The majority of the ouabain-insensitive K influx in human erythrocytes is
dependent on the presence of Cl. Recent studies have shown that a portion
of the Cl-dependent K influx persists in the absence of external Na (Nao).
It has been suggested that this Nao-independent component represents (K +
Cl) cotransport, whereas the remainder of the Cl-dependent K influx seen on
addition of external Na represents (Na + K + 2Cl) cotransport. In the
present studies, the kinetics of Cl-dependent K influx were examined in the
presence and absence of external Na, by varying external K and external Cl.
Our studies suggest that the Nao-independent Cl-dependent pathway has a
relatively low affinity for external K (Km 17-30 mM) in contrast to the
high affinity of the Nao-augmented component (Km 3-4 mM). N-ethylmaleimide
(NEM) stimulates the maximal velocity of the Nao-independent Cl-dependent K
influx achievable without alteration of intracellular solutes but does not
alter its Km for external K. In contrast, NEM has no stimulatory effect on
the Nao-augmented component. The Cl dependence of the Nao-independent K
influx is best described by a relatively flat curve with a mild upward
concavity. The kinetic properties of the Nao-independent component of
Cl-dependent K transport are very similar to those of the putative (K + Cl)
cotransport pathway seen in low-K sheep erythrocytes.(ABSTRACT TRUNCATED AT
250 WORDS)
