Multiple action sites of flufenamate on ion transport across the rat distal colon

1 The antisecretory effects of flufenamate in the rat distal colon were inv estigated with the Ussing-chamber and the patch-clamp method as well as by measurements of the intracellular Ca2+ concentration using fura-2-loaded is olated crypts. 2 Flufenamate (5 . 10(-4) mol l(-1)) suppressed the short-circuit current ( Isc) induced by carbachol (5 . 10(-5) mol l(-1)), forskolin (5 . 10(-6) mol l(-1)) and the Isc induced by the membrane-permeable analogue of cyclic AM P, CPT-cyclic AMP (10(-4) mol l(-1)). 3 Indomethacin (10(-6)-10(-4) mol l(-1)) did not mimic the effect of flufen amate, indicating that the antisecretory effect of flufenamate is not relat ed to the inhibition of the cyclo-oxygenase. 4 When the basolateral membrane was depolarized by a high K+ concentration and a Cl- current was induced by a mucosally directed Cl- gradient, the for skolin-stimulated Cl- current was blocked by flufenamate, indicating an inh ibition of the cyclic AMP-stimulated apical Cl- conductance. 5 When the apical membrane was permeabilized by the ionophore, nystatin, fl ufenamate decreased the basolateral K+ conductance and inhibited the Na+-K-ATPase. 6 Patch-clamp experiments revealed a variable effect of flufenamate on memb rane currents. In seven out of 11 crypt cells the drug induced an increase of the K+ current, whereas in the remaining four cells an inhibition was ob served. 7 Experiments with fura-2-loaded isolated crypts indicated that flufenamate increased the basal as well as the carbachol-stimulated intracellular Ca2 concentration. 8 These results demonstrate that flufenamate possesses multiple action site s in the rat colon: The apical Cl- conductance, basolateral K+ conductances and the Na+-K+-ATPase.