Active Transport of Sodium by the Isolated Midgut of Hyalophora Cecropia

Sodium and lithium are actively transported by the isolated midgut of Hyalophora cecropia. The short-circuit current in 32 mM sodium solution is about half of that in 32 mm potassium solution. The sodium flux measured with 22Na from blood-side to lumen accounts for all of the short-circuit current and is 19 times the flux from lumen to blood-side. In a solution containing 16 mm potassium and 16 mm sodium there is no transport of sodium, although a large current remains. The sodium transport mechanism is not sensitive to ouabain.