The Journal of General Physiology, Vol 68, 567-581, Copyright © 1976 by The Rockefeller University Press
Passive potassium transport in LK sheep red cells. Effects of anti-L antibody and intracellular potassium
PB Dunham
The passive K influx in low K(LK) red blood cells of sheep saturates with
increasing external K concentration, indicating that this mode of transport
is mediated by membrane-associated sites. The passive K influx, iMLK, is
inhibited by external Na. Isoimmune anti-L serum, known to stimulate active
K transport in LK sheep red cells, inhibits iMLK about twofold. iMLK is
affected by changes in intracellular K concentration, [K]i, in a complex
fashion: increasing [K]i from near zero stimulates iMLK, while further
increases in [K]i, above 3 mmol/liter cells, inhibit iMLK. The passive K
influx is not mediated by K-K exchange diffusion. The effects of anti-L
antibody and [K]i on passive cation transport are specific for K: neither
factor affects passive Na transport. The common characteristics of passive
and active K influx suggest that iMLK is mediated by inactive Na-K pump
sites, and that the inability to translocate Na characterizes the inactive
pumps. Anti-L antibody stimulates the K pump in reticulocytes of LK sheep.
However, anti-L has no effect on iMLK in these cells, apparently because
reticulocytes do not have the inactive pump sites which, in mature LK
cells, are a consequence of the process of maturation of circulating LK
cells. The results also indicate that anti-L alters the maximum velocity of
both active and passive K fluxes by converting pumps sites from a form
mediating passive K influx to an actively transporting form.
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