SODIUM-INDEPENDENT ACTIVE TRANSPORT OF POTASSIUM IN THE ISOLATED MIDGUT OF THE CECROPIA SILKWORM

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Abstract
The lumen of an isolated larval midgut is 84 mV positive to the blood side. Potassium diffusion potentials contribute to but do not account for the trans-midgut potential. The potassium-42 flux toward the lumen is 32 times greater than predicted from the electrochemical potential. At least 87% of the short-circuit current is carried by potassium moving toward the lumen. Apparently, sodium plays no role in this active potassium transport since similar potential differences, short-circuit currents, and potassium fluxes are obtained with or without sodium.