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Journal of Experimental Biology 77,107-122 (1978)
Published by Company of Biologists 1978

The Source of Short-Circuit Current Across Locust Rectum

D. WILLIAMS ¹, J. E. PHILLIPS ¹, W. T. PRINCE ¹, and J. MEREDITH ¹

¹ Department of Zoology, University of British Columbia, Vancouver, B.C., Canada V6T 1W5

Recta of desert locusts were mounted as flat sheets in ‘Ussing-type’ chambers and various parameters of tissue viability were monitored. The trans-epithelial resistance, the electropotential difference, the short-circuit current (I_sc), and unidirectional fluxes of ²²Na⁺, ³⁶C1^- and ⁴²K⁺ all remained relatively constant during the 3rd and 4th h.

The direction of the I_sc indicated a net transport of either anions to the haemocoel, or cations to the lumen side. This current was abolished by KCN and was sensitive to temperature (Q₁₀ = 2.4).

There was a rapid decline in I_sc over the first 2 h, which could be abolished by substituting NO₃^- or SO₄^2- for Cl^- in the bathing medium, indicating that this fall in current is due to a decline in the rate of Cl^- transport. Measurements of ³⁶C1^- fluxes under short-circuit conditions confirm this interpretation.

In the steady-state (3rd and 4th h), however, the same anion substitutions had no effect on I_sC. Concurrent flux measurements indicated that net Na⁺ and K⁺ transport to the haemocoel side equals or slightly exceeds that of C1^- in the same direction. Consequently all of the I_sc must be due to unidentified ion transport processes. Transport of H⁺ to the lumen, or HCO₃^- and organic anions to the haemocoel side, is proposed.