AJP - Cell Physiology, Vol 263, Issue 5 C1007-C1014, Copyright © 1992 by American Physiological Society
Rat kidney Na-K pumps incorporated into low-K+ sheep red blood cell membranes are stimulated by anti-Lp antibody
Z. C. Xu, P. B. Dunham, J. S. Munzer, J. R. Silvius and R. Blostein
Department of Medicine, McGill University, Montreal, Quebec, Canada.
A genetic dimorphism of sheep red blood cells characterized by differences
in the intracellular K+ concentration of mature red blood cells (low-K+ or
high-K+ cells) reflects differences in their Na-K pumps and is known to be
linked to the ML blood group system. We investigated the relationship of
Na-K pumps in red blood cells from sheep of the low-K+ phenotype with an
antigen, Lp, that is restricted to low-K+ cells. Anti-Lp antibody
stimulates the Na-K pumps in these cells presumably by relieving inhibition
of the pumps by Lp. The questions addressed were as follows: is Lp a
molecular entity distinct from pumps and, if so, can it interact with pumps
of exogenous origin? Rat kidney Na-K pumps were incorporated by fusion of
microsomes into either low-K+ or high-K+ sheep red blood cells. The
activity of the exogenous kidney pumps was distinguished from that of the
endogenous red blood cell pumps by the low sensitivity of rodent pumps to
ouabain. Anti-Lp stimulated by > 50% rat kidney pumps incorporated into
immature low-K+ sheep cells. This indicates that Lp is a distinct molecular
entity free to dissociate from endogenous pumps and inhibit exogenous
pumps. Anti-Lp did not stimulate kidney pumps incorporated into mature
low-K+ cells but did stimulate kidney pumps following in vitro maturation
of microsome fused reticulocytes, probably reflecting restriction of
lateral movement of pumps and antigens by the cytoskeleton in mature cells.
