AJP - Renal Physiology, Vol 251, Issue 4 702-F709, Copyright © 1986 by American Physiological Society
Electrically neutral Na+-H+ exchange in endosomes obtained from rabbit renal cortex
R. W. Gurich and D. G. Warnock
Endocytotic vesicles (i.e., endosomes) were prepared from rabbit renal
cortex following the intravenous injection of horseradish peroxidase. The
endosomal population was derived from a 100,000-g pellet and was found at
equilibrium in the lightest area of a sucrose density gradient. This
population was separate from other organelles as determined by enzyme
markers and had a 2.5-fold enrichment of horseradish peroxidase specific
activity compared with the homogenate specific activity corrected for
soluble horseradish peroxidase activity. The endosomes contain an
oligomycin-insensitive, electrogenic H+-translocating ATPase. They also
contain an electroneutral Na+-H+ exchanger. This exchanger is not inhibited
by amiloride, and lithium is not a substrate for the exchanger. Lithium
does inhibit the Na+-H+ exchanger when added prior to the addition of
sodium. The Michaelis constant for sodium of the endosomal Na+-H+ exchanger
was found to be 10.0 mM. These data indicate that a population of endosomes
from rabbit renal cortex contain an electrogenic H+-ATPase and an
electroneutral Na+-H+ exchanger and that the exchanger is distinct from the
brush-border membrane Na+-H+ antiporter.
