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Journal of Experimental Biology 137,341-360 (1988)
Published by Company of Biologists 1988

Sodium-Independent Proline Transport in the Locust Rectum

J. Meredith ¹ and J. E. Phillips ¹

¹ Department of Zoology, University of British Columbia, Vancouver, BC, V6T2A9, Canada

To whom reprint requests should be addressed.

1. Recta of Schistocerca gregaria possess a high-affinity (K_t = 10 mmol 1^-1) and high-capacity (V_max = 4.2 µequiv cm^-2h^-1) active absorptive mechanism for proline second in magnitude only to stimulated Cl^- transport.

2. Transcellular and paracellular pathways have extremely low passive permeability to proline, resulting in very high flux ratios (40:1) compared with those for other.solutes (less than 6:1).

3. Net epithelial transport of proline is largely independent of luminal Na⁺, K⁺ and Cl^-. Sodium influx does not change when proline net fluxes are varied 14-fold. Therefore Na⁺ cotransport is not a principal mechanism of proline uptake in this tissue.

4. Prolonged absence of Na⁺ and K⁺ from the haemocoel side partially inhibits proline transport, probably indirectly, by affecting the general transport capacity of the rectum. Inhibition is irreversible.

5. A component of the net proline flux (J_net^pro) is electrogenic, located in the apical membrane, and may be due to proline/proton cotransport.

Key words: proline, amino acid transport, Na⁺ cotransport, locust rectum.

Accepted on January 6, 1988