Electrogenic, K⁺-dependent chloride transport in locust hindgut

Potassium chloride is the major salt recycled in most insect excretory systems. Ion and water reabsorption occur in the rectum by active transport of Cl$^-$ and largely passive movement of K$^+$. Both these processes are stimulated several fold by a neuropeptide hormone acting via cyclic AMP (cAMP). This Cl$^-$ transport process was investigated by using intracellular ion-sensitive microelectrodes, radiotracer flux measurements, voltage clamping, ion substitutions and inhibitors. The mucosal entry step for Cl$^-$ is energy-requiring and highly selective, and is stimulated directly by cAMP and luminal K$^+$. Under some experimental conditions, measured electrochemical potentials for cations across the mucosal membrane are too small to drive Cl$^-$ entry by NaCl or KCl cotransport mechanisms; moreover, net $^{36}$Cl$^-$ flux is independent of the apical Na$^+$ potential. Similarly no evidence for a HCO$^-_3$-Cl$^-$ exchange was obtained. We conclude that Cl$^-$ transport in locust gut is different from mechanisms currently proposed for vertebrate tissues.