Functional differences between the rabbit and human na+/
dicarboxylate cotransporters expressed in xenopus oocytes.
Pajor, Ana M., and Ning Sun.
University of Arizona, Department of Physiology, College of
Medicine, Tucson, AZ 85724
APStracts 3:0151F, 1996.
The rabbit and human Na+/dicarboxylate cotransporters, NaDC-1 and
hNaDC-1, were expressed in Xenopus oocytes and the transport of
succinate, citrate and glutarate was compared. Both transporters had
similar affinities for succinate and glutarate, with Km's of about
0.5-0.8 mM (succinate) and 6-7 mM (glutarate), verifying that they
are low affinity sodium-dependent dicarboxylate transporters. The two
transporters differed in their handling of citrate. At pH 7.5, the Km
for citrate was 0.9 mM in the rabbit NaDC-1 and 7 mM in the human
hNaDC-1. However, the human transporter was more sensitive to pH than
the rabbit. At pH 5.5, the Km for citrate decreased to 1.2 mM in
hNaDC-1 and decreased to 0.3 mM in the rabbit transporter. Both
transporters had Hill coefficients between 1.6 and 2.1, suggesting
that multiple sodium ions are coupled to the transport of divalent
anions. However, the human transporter, hNaDC-1, had a lower apparent
affinity for sodium (KNa 78 mM) than the rabbit transporter (KNa 41
mM). In addition, the human hNaDC-1 was relatively insensitive to
inhibition by lithium, furosemide and flufenamate compared with the
rabbit NaDC-1. The differences between the human and rabbit
transporters may account for observed differences in renal handling
of citrate between species.
Received 14 March 1996; accepted in final form 22 August 1996.
APS Manuscript Number F96-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996