AJP - Cell Physiology, Vol 253, Issue 2 C199-C204, Copyright © 1987 by American Physiological Society
Inhibition by amiloride analogues of Na+-dependent hexose uptake in LLC-PK1/Cl4 cells
J. S. Cook, C. Shaffer and E. J. Cragoe Jr
Amiloride and four analogues of amiloride were shown to inhibit
Na+-dependent, phlorizin-sensitive hexose uptake by a clone of pig kidney
cells, LLC-PK1/Cl4. The analogues tested were:
5-(N-ethyl-N-isopropyl)amiloride (EIPA), 5-(N-methyl-N-isobutyl)amiloride
(MIBA), 3',4'-dichlorobenzamil, and phenamil. The transport substrate was
the nonmetabolizable glucose analogue alpha-methyl-D-glucoside. Blockade of
Na+-K+ transport at the basolateral membranes or removal of divalent
cations from the assay medium had little effect on the initial rate of
hexose uptake, whereas MIBA remained an effective inhibitor under both
conditions. The inhibitions by EIPA of Na+-H+ exchange and hexose-dependent
Na+ uptake could be distinguished by appropriate choice of concentrations
of the inhibitor. Hexose transport inhibition does not appear to be
secondary to other known effects of the amilorides. Inhibition by all
analogues is enhanced when they are tested in low (2 mM) Na+ medium, where
they show half-maximal inhibition in the range of 100-300 microM. More
detailed kinetic analysis of inhibition by EIPA shows it to be competitive
with Na+ with a Ki of 73-107 microM. It is concluded that the amilorides
are acting directly on the hexose transporter.
