AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 6 1539-R1545, Copyright © 1995 by American Physiological Society
Relation of membrane potential to basolateral TEA transport in isolated snake proximal renal tubules
Y. K. Kim and W. H. Dantzler
Department of Physiology, College of Medicine, University of Arizona, Tucson 85724, USA.
We measured the effects of changes in bath K+ concentration ([K+]) on
basolateral membrane potential difference (PD) and [3H]tetraethylammonium
(TEA) transport in isolated snake (Thamnophis) proximal renal tubules (25
degrees C; pH 7.4). Increasing bath [K+] from 3 to 65 mM decreased PD from
-60 mV (inside of cells negative) to -20 mV and 2-min uptake of [3H]TEA by
approximately 25%, indicating that PD influences TEA entry into the cells.
Uptake of [3H]TEA was inhibited similarly at both K+ concentrations by
unlabeled TEA, indicating that uptake is carrier mediated. Kt
(approximately 18 microM) for 2-min uptake of [3H]TEA in 3 mM K+ increased
significantly in 65 mM K+, suggesting that the decrease in PD or the
increase in [K+] alters the affinity of the transporter for TEA. The
steady-state cell-to-bath ratio for [3H]TEA with 3 mM K+ (-60 mV PD) was
approximately 16, significantly above the ratio of 10 predicted for passive
distribution at electrochemical equilibrium. With 65 mM K+ (-20 mV PD) this
ratio decreased to approximately 6, again significantly above the predicted
ratio of 2. These data suggest that the PD can account for much, but not
all, of the steady-state uptake of TEA. Efflux of [3H]TEA across the
basolateral membrane was identical with either 3 or 65 mM K+ in the bath
but was almost completely inhibited in either case by tetrapentylammonium,
a potent inhibitor of TEA uptake. These data indicate that virtually all
TEA transport across the basolateral membrane is carrier mediated and that
transport out of the cells is unaffected by PD.
