Na+/h+ exchange modulates acidification of early rat liver
endocytic vesicles.
Vandyke, Rebecca W., Tammie L. Bully, and Kimberly K. Belanger.
Veterans Administration Medical Center, Gastroenterology Division
and Department of Internal Medicine, University of Michigan Medical
School, Ann Arbor, MI 48109-0682
APStracts 2:0198C, 1995.
Endocytic vesicles are acidified by an electrogenic vacuolar H+
-ATPase. These studies examined whether rat liver endosomes also
exhibit Na+/H+ exchange and whether this transporter alters
acidification. Extravesicular Na+ caused saturable proton efflux from
acidified endosomes with a Km for Na+ of 7.6 mM, whereas an in-to-out
Na+ gradient caused endosome acidification without MgATP and
accelerated acidification with MgATP. Na+-driven proton fluxes were
little altered by valinomycin or carbonyl cyanide m
-chlorophenylhydrazone. Na+/H+ exchange was inhibited by Li+ but was
not affected by K+, Cl-, amiloride (1 mM) or 5-(N, N-dimethyl)
amiloride (0.1 mM). Na+/H+ exchange was detected in "early"
but not in "late" liver endosomes or in lysosomes. These data
suggest that early rat liver endosomes exhibit Na+/H+ exchange that,
immediately after endosome formation, may accelerate vesicle
acidification. Because of its insensitivity to amiloride, this
exchanger may be a pharmacologically altered form of NHE-1 or a new
isoform.
Received 27 January 1995; accepted in final form 5 May 1995.
APS Manuscript Number C52-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.