Specificity of basolateral organic cation transport in snake renal
proximal tubules.
Kim, Yung Kyu, and William H. Dantzler.
Department of Physiology, College of Medicine, University of
Arizona, Tucson, Arizona 85724
APStracts 2:0313R, 1995.
We examined the specificity of basolateral organic cation transport in
isolated snake (Thamnophis spp.) renal proximal tubules by
determining the inhibitory effect of a series of n-tetraalkylammonium
(n-TAA) compounds (n = 1-5) on the basolateral uptake of
[3H]tetraethylammonium (TEA). The inhibitory potency increased with
increasing alkyl chain length, the apparent Michaelis constants for
inhibition of TEA uptake ranging from 3.3 mM for tetramethylammonium
(TMA) to 1.0 _M for tetrapentylammonium (TPeA). Thus the apparent
affinity of the carrier for n-TAA compounds increases with their
increasing hydrophobicity. Because previous data suggested that TEA
transport across the basolateral membrane may be asymmetrical and
that the exit step may be regulated differently from the entry step,
we examined the kinetics of [3H]TEA efflux across the basolateral
membrane. Efflux, like entry, occurred by a saturable process that
could be described adequately by Michaelis-Menten kinetics. However,
the Kt for efflux (110 _M) was about six times the Kt for uptake (18
_M), indicating that the affinity of the carrier for TEA is greater
in the uptake direction than in the efflux direction or that there
are separate carriers with different affinities for uptake and
efflux. In either case, this difference would favor movement of TEA
taken up at the basolateral side across the cells and into the lumen
over movement back into the peritubular fluid.
Received 27 July 1995; accepted in final form 7 November 1995.
APS Manuscript Number R459-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95