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  1. 1.

    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.

  2. 2.

    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).

  3. 3.

    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.

  4. 4.

    Acetate saline sustains ISC, PD and transepithalial resistance (R) at higher levels than does simple Cl-saline.

  5. 5.

    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.

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