| Summary: | Rectum trammural potential (PD) and short-circuit current (Isc) of the desert locust,
Schistocercu 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 Isc of about
300 4 cm-* 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 IBC. 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 IW 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.
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