Transport characteristics of the isolated rectal complex of the mealworm Tenebrio molitor

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Abstract
The coupling between water and ion transport in the rectal complex of mealworms can be studied further using an in vitro preparation under oil. Preliminary investigations into the properties of such a preparation are described. The preparation remains viable over several hours when sustained with transportable cations, primarily potassium but not sodium, which appears to be the limiting factor in generating long-term water absorption. Potassium is selectively transported by the Malpighian tubules surrounding the rectum, thus generating osmotic forces necessary for water absorption from within the lumen. Reabsorption was studied using sucrose solutions of different concentrations in the rectal lumen. The preparation absorbed water from extremely low water activities down to the same threshold value (aw = 0.88) observed in intact animals. Absorption rates were less than half those observed in vivo, probably because of the viscosity of the sucrose solutions. Transported water emerging from the common duct of the preparation included a significant contribution from the haemolymph.