Composition of fluid transported by locust ileum: influence of natural stimulants and luminal ion ratios

Abstract

Unstimulated fluid transport by everted locust ileal sacs in vitro was supported at 50% of control levels by the presence externally of any one of Na+, K+, or Cl−, whereas removal of all but trace levels of these ions reduced fluid transport to 25% of control transport rates. Stimulation of fluid transport by corpus cardiacum or fifth ventral ganglion extracts did not occur unless Cl− was present. The presence of Na+ or K+ was also required for maximum stimulation of fluid transport by these factors, the greatest stimulation occurring when the Na+:K+ ratio was 1:1. Cyclic AMP, and corpus cardiacum and fifth ventral ganglion extracts all stimulated Na+, Cl−, and K+ absorption across everted ileal sacs. Stimulation of fluid transport by these factors largely eliminated the anion deficit (Na+ + K+−Cl−) observed under unstimulated conditions. Stimulation caused large decreases in absorbate [Formula: see text] concentrations and pH concurrent with the increased absorbate Cl− levels. These results indicate a switch from low-capacity NaHCO3 plus NaCl transport under unstimulated conditions to high-capacity NaCl transport under stimulated conditions. Stimulation of fluid transport also causes a 3-fold increase in transepithelial potential (hemocoel negative), indicating stimulation of electrogenic anion (Cl−) movement to the hemocoel. These results provide the first direct evidence for hormonal control of Na+ reabsorption in insect excretory systems.

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

“…Indeed, LocmiFGLa/AST-2 at 10 −10 mol l −1 inhibited uptake of water by 47% over 60 min. The water uptake rates found here (3 μl h −1 ) are the same as those observed by Lechleitner et al (Lechleitner et al, 1989) in S. gregaria, and confirms the viability and robustness of this in vitro ileum preparation from L. migratoria. FGLa/ASTs have previously been implicated in the modulation of ion transport in insects.…”

The effect of cold acclimation on active ion transport in cricket ionoregulatory tissues

“…First, active transport across the rectal pads of warm-and cold-acclimated insects should be compared (e.g. via Ussing chamber; Ussing and Zerahn, 1951;Clarke, 2009 or everted-sac technique (Barthe et al, 1998;Lechleitner et al, 1989) to determine whether rectal transport is modified by cold acclimation overall. The specific enzymatic targets of cold acclimation (and their relative contribution to altered transport function) could then be determined by comparing active transport rates across the rectum with and without selective enzyme inhibitors (Bertram et al, 1991;Clarke, 2009;Hanrahan et al, 1984).…”

Insect ion transport peptides are derived from alternatively spliced genes and differentially expressed in the central and peripheral nervous system

“…Peptidic or proteinaceous factors have been detected in the brain and CC and in the ventral nerve cord (VNC; e.g. locust abdominal ganglia 4 to 7) (Audsley and Phillips, 1990) that dose-dependently stimulate ileal I sc and water fluxes (Lechleitner et al, 1989b;Lechleitner and Phillips, 1989). These physiological events are known to be driven by an apical chloride pump electrically coupled predominantly to potassium but also to sodium as passive followers (Phillips et al, 1986;Phillips et al, 1996;Phillips et al, 1998a), the first description of which became a recent JEB citation classic (Bradley, 2008).…”