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The unidirectional fluxes of 36Cl− and 22Na+ across short-circuited locust recta bathed in a simple NaCl saline were followed with time. Unidirectional fluxes and net flux of 22Na+ to the haemocoel side all remained constant for at least 4 h and were unaffected by either corpora cardiaca homogenate (CC) or cAMP.
Both CC and cAMP stimulated influx and net flux of 36Cl− to the haemocoel side. Over the whole time course of the experiment, i.e. both before and after stimulation, net Cl− flux approximately equalled the shortcircuit current (ISC).
Neither CC nor cAMP caused substantial stimulation of ISC or transepithelial electropotential difference (PD) if all Cl− in the bathing saline was replaced by either sulphate or nitrate or acetate.
Acetate saline sustains ISC, PD and transepithalial resistance (R) at higher levels than does simple Cl-saline.
Experiments with Cl-free, SO4-salines suggest that alternate electrogenic transport processes can be slowly turned on when Cl− is absent, provided a complex saline which contains several organic constituents, or simple acetate saline, is present.