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Recta of Schistocerca gregaria possess a high-affinity (Kt = 10 mmol 1−1) and high-capacity (Vmax = 4.2 μequiv cm−2h−1) active absorptive mechanism for proline second in magnitude only to stimulated Cl− transport.
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).
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.
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.
A component of the net proline flux (Jnetpro) is electrogenic, located in the apical membrane, and may be due to proline/proton cotransport.