Active Potassium Transport by the Isolated Lepidopteran Larval Midgut: Stimulation of Net Potassium Flux and Elimination of the Slower Phase Decline of the Short-Circuit Current Available to Purchase

Adenosine 3’:5’-cyclic monophosphate (cyclic AMP), Antibiotic A23187, caffeine, cholera toxin, dibutyryladenosine 3’ :5’-cyclic monophosphate (dbcAMP), 5-hydroxytryptamine (5-HT), larval blood, and theophylline were tested for their effects on active potassium transport, as measured by the short-circuit current (SCC), in isolated Manduca sexta larval midgut.

None of the tested materials affected the short-circuit current during the rapid phase of its usual exponential decline, and only dbcAMP and larval blood affected the short-circuit current during the slower phase of its exponential decline.

Dibutyryl-cyclic AMP stimulated an increase in short-circuit current and net potassium flux (measured using ⁴²K). Both unidirectional potassium fluxes increased but there was no effect on the flux ratio or on the rate at which net potassium transport declined with time.

A dialysable extract of fifth instar larval blood effected potassium transport in a manner similar to that of dbcAMP, indicating that larval blood contains natural transport-stimulating factors.

A dialysable extract of fourth instar larval blood not only stimulated potassium transport but also prevented the slow phase of decline in the short-circuit current. Therefore, in addition to transport-stimulating factors present in fifth instar blood, fourth instar blood appears to contain substances which prevent degeneration of at least the transport related functions of midgut in vitro.

It is argued that the action of the transport-stimulating factor in larval blood on the electrogenic cation pump in larval midgut cells is mediated by cyclic AMP without involving a change in intracellular calcium ion concentration.