Inhibiting conductive Cl uptake in membrane vesicles: specificity of alpha-phenylcinnamate.
alpha-Phenylcinnamate has been investigated in comparison to other inhibitors of chloride ion transport into porcine jejunal brush-border membrane vesicles. The transport modes studied included uptake driven only by a chemical Cl gradient, Cl uptake dependent on a transmembrane potential, self-exchange of Cl with no chemical or potential gradient, and Cl uptake dependent on a chemical gradient for bicarbonate. Uptake driven by the chemical gradient for Cl was strongly inhibited by millimolar concentrations of diphenylamine-2-carboxylate, 5-nitro-2-(2-phenylethylamino)benzoate (NPEB), and to a lesser extent by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). Similar concentrations of alpha-phenylcinnamate did not reduce this mode of Cl uptake. Conductive Cl uptake driven by a potassium gradient was inhibited by approx. 50% at 2.5 mM alpha-phenylcinnamate. alpha-Phenylcinnamate was equally effective in reducing the initial rate of conductive chloride accumulation in vesicles with naturally opened Cl channels (conductance activation by cyclic AMP and Ca2+), or with Cl channels opened by exposure to tetramethylammonium (TMA) buffer. In comparison with diphenylamine-2-carboxylate, NPEB and SITS, alpha-phenylcinnamate had the least effect on Cl-HCO3 exchange at inhibitor concentrations which reduced conductance activity. Self-exchange rates of physiological concentrations of Cl were also relatively unaffected by low mM concentrations of alpha-phenylcinnamate. Kinetic analysis indicated that alpha-phenylcinnamate was an uncompetitive inhibitor, requiring the presence of the normal Cl ligand for binding to, and inhibition of, conductive Cl transport by pig intestinal brush-border vesicles.
Forsyth
G W
GW
Veterinary Physiological Sciences, University of Saskatchewan, Saskatoon, Canada.
Gabriel
S E
SE
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D002934:Cinnamates / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D013552:Swine
D002712:Chlorides; D002934:Cinnamates; C061614:alpha-phenylcinnamate