K+ absorption by locust gut and inhibition of ileal K+ and water transport by FGLamide allatostatins.

Abstract

Abstract The Scanning Ion-Selective Electrode Technique (SIET) was utilized for the first time in Locusta migratoria to characterize K+ transport along the digestive tract and to determine the effect of two locust FGLamide allatostatins (FGLa/ASTs) on K+ transport: a previously sequenced FGLa/AST from Schistocerca gregaria (Scg-AST-6; ARPYSFGL-NH2) and a newly sequenced FGLa/AST from L. migratoria (Locmi-FGLa/AST-2; LPVYNFGL-NH2). Regional differences in K+ fluxes along the gut were evident, where K+ efflux in vitro (or absorption into the hemolymph in vivo) was greatest at the anterior ileum, and lowest at the colon. Ileal K+ efflux was inhibited by both Scg-AST-6 and Locmi-FGLa/AST-2, with maximal inhibition at 10-10 and 10-11 M, respectively. Both FGLa/ASTs also inhibited cAMP-stimulated K+ efflux from the ileum. Locmi-FGLa/AST-2 also inhibited efflux of water across the ileum. Locusts are terrestrial insects living in dry climates, risking desiccation and making water conservation a necessity. The results suggest that FGLa/ASTs may be acting as diuretics by increasing K+ excretion and therefore increasing water excretion. Thus, it is likely that FGLa/ASTs are involved in the control of hemolymph water and ion levels during feeding and digestion, to help the locust deal with the excess K+ load (and subsequently fluid) when the meal is processed.