Chloride-dependent transmural potential in the rectal wall of Schistocerca gregaria

Abstract

Rectum transmural potential (PD) and short-circuit current ( I sc) of the desert locust, Schistocerca gregaria, have been studied in vitro, with everted rectal wall preparations in solutions of different ionic composition. Initially, a PD of about 35 mV (lumen positive) and a I sc of about 300 μA cm −2 were recorded. Omission of sodium or potassium (Tris as substitute), from the luminal side or from both sides led to an increase of 4 to 6 mV in PD (lumen more positive) together with an increase in I sc. In the absence of chloride alone (sulphate as substitute) the PD quickly dropped to nearly zero. In each case the control values were recovered on replacing the corresponding ions. Neither the PD nor the I sc changed when substitutions affected only the haemocoelic solution. These findings corroborate the assumption that active transport of chloride ions from lumen to haemolymph is the major factor for transmural PD and account for the short-circuit current in the rectal wall of desert locust. A working scheme is given to explain the influence of sodium, potassium, and chloride ions on the PD.