Transport of Thallium Ions Across the Isolated Midgut of Hyalophora Cecropia

T1+ permeates the Hyalophora cecropia midgut equally in both directions, but the flux of Tl+ per mm is up to 50 times higher than the passive flux for potassium, rubidium and caesium. This is explained by assuming that the T1+ flux is a carrier-mediated facilitated diffusion or a passage through channels similar to gramicidin channels in black membranes. We have found this special way for Tl+ to pass through membranes in the Hyalophora cecropia midgut; some other membranes, such as red blood cells, seem to show the same properties, but others, such as frog muscle and skin, do not.