Anion selectivity of the chloride-transport process in dog tracheal epithelium.

We have measured the fluxes of 82Br or 131I across short-circuited dog tracheal epithelium following complete replacement of chloride in the bathing medium by either bromide or iodide. In addition, we have partly replaced the bathing chloride with bromide, iodide, or thiocyanate and studied the effects of these anions on 36Cl fluxes. Our results show that the affinity sequence for the chloride transport process is I > Br congruent to Cl, that Br is transported, but that I is not. Thiocyanate is a potent inhibitor of chloride transport, and its effects are greater than those predicted by a simple competitive interaction with chloride for transport sites.