Demonstration of a pump-mediated efflux in the epithelial potassium active transport system of insect midgut.

The larval midgut epithelium of lepidopteran insects (e.g., Hyalophora cecropia and Manduca sexta) actively transports potassium from hemolymph to lumen when mounted in a chamber. The potassium active transport is rheogenic and does not require the presence of other alkali ions. The transepithelial potential difference, short-circuit current, and electromotive force of active transport are rapidly diminished by anoxia. The efflux of potassium, opposite in direction to potassium active transport, dramatically increased in anoxia, whereas the effluxes of sodium, cesium, and chloride did not increase in anoxia. The increase in efflux was found to have an alkali selectivity similar to that of potassium active transport. It is concluded that the rise of efflux in anoxia is due to the change characteristics of the epithelial potassium active transport mechanism in anoxia.