The insect V-ATPase, a plasma membrane proton pump energizing secondary active transport: molecular analysis of electrogenic potassium transport in the tobacco hornworm midgut

Goblet cell apical membranes in the larval midgut of Manduca sexta are the site of active and electrogenic K⁺ secretion. They possess a vacuolar-type ATPase which, in its immunopurified form, consists of at least nine polypeptides. cDNAs for the A and B subunits screened by monoclonal antibodies to the A subunit of the Manduca V-ATPase or by hybridisation with a cDNA probe for a plant V-ATPase B subunit have been cloned and sequenced. There is a high degree of identity to the sequences of the respective subunits of other V-ATPases.

The M. sexta plasma membrane V-ATPase is an electrogenic proton pump which energizes, by the electrical component of the proton-motive force, electrogenic K⁺/nH⁺ antiport, resulting in net electrogenic K⁺ secretion. Since the midgut lacks a Na⁺/K⁺-ATPase, all solute fluxes in this epithelium seem to be energized by the V-ATPase. Thus, the midgut provides an alternative to the classical concept of animal plasma membrane energization by the Na⁺-motive force generated by the Na⁺/K⁺-ATPase.