Triaminopyrimidinium (TAP+) blocks luminal membrane K conductance in Necturus gallbladder epithelium

The effect of triaminopyrimidinium (TAP+) on the apical membrane of necturus gallbladder epithelial cells was investigated with intracellular microelectrode techniques. TAP+, added to the mucosal bathing solution only, produced the following effects (all rapid and reversible): (i) cell depolarization, (ii) increase of apical membrane resistance, and (iii) decrease of the apical membrane potential change produced by K for Na substitution on the mucosal side. These results can be explained by a decrease of apical membrane K conductance. The paracellular effects of TAP+ were similar to the ones previously described by Moreno (J.H. Moreno, 1974; Nature (London) 251:150; J.H. Moreno, 1975. J. Gen. Physiol. 66:97). These results indicate that the change of transepithelial potential produced by TAP+ cannot be ascribed solely to its effect on the paracellular pathway.