Routes of nonelectrolyte permeability in gallbladder. Effects of 2,4,6-triaminopyrimidinium (TAP).

The organic cation 2,4,6-triaminopyrimidinium (TAP), which blocks the tight junction channels for cation permeability across gallbladder, also inhibits gallbladder permeability (P) to urea and glycerol without significantly affecting P to Cl(-), sucrose, 1,7-heptanediol, or water (osmotic or diffusional permeabilities). These effects together with the comparisons of P's in frog with P's in rabbit gallbladder suggest that sucrose migrates exclusively through the leakage pathway (through where Cl(-) permeates), and that urea and glycerol permeate in addition through both, the tight junction channels for cations and a polar pathway at the cell membranes. Water and 1,7-heptanediol probably permeate mainly through the epithelial cell membranes.