Interaction of akg with basolateral organic anion transporter in
isolated rabbit renal s3 proximal tubules .
Shpun, Shlomo, Kristen K. Evans, and William H. Dantzler.
Department of Physiology, College of Medicine, University of
Arizona, Tucson, Arizona
APStracts 2:0020F, 1995.
To understand the basolateral para-aminohippurate (PAH) transporter in
the S3 segment of rabbit proximal tubules and its relationship to the
transporter in the S2 segment, we measured the 30 s uptake and efflux
of PAH across the basolateral membrane of single isolated S3 segments
at 37 degrees C in bicarbonate-buffered media. Kinetic analysis of uptake
data revealed a Kt of 107 mM (same as in the S2 segment) but a Jmax
of 600 fmol min-1 nl-1 (1/10 that of S2 segment). The coefficient for
efflux across the basolateral membrane was also only 1/6 to 1/10 of
that in the S2 segment. These data suggest that the basolateral PAH
transporter is the same in both segments but that there are fewer
transporters in the S3 than in the S2 segment. However, the apparent
Ki values for cis-inhibition by probenecid (29 mM in S3; 15 mM in S2)
and by a-ketoglutarate (aKG) in the presence of LiCl (40 mM in S3;
160 mM in S2) suggest that the transporters may not be identical in
the two segments. In bicarbonate-buffered medium, preloading the
tubules with 100 mM aKG did not trans-stimulate PAH uptake across the
basolateral membrane, whereas preloading with 1.0 mM aKG caused a
significant stimulation of 43%. However, in HEPES-buffered medium,
preloading the tubules with 100 mM aKG caused a two-fold increase in
PAH uptake. These data suggest that the initial intracellular
concentration of aKG (or metabolic state of the tubule) may influence
PAH uptake and the trans-stimulatory effect of aKG.
Received 12 September 1994; accepted in final form 3 January
1995.
APS Manuscript Number F328-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.