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Updated: Jul 30, 2026

Use of the Ramsay Assay to Measure Fluid Secretion and Ion Flux Rates in the Drosophila melanogaster Malpighian Tubule
Published on: November 25, 2015
The permeability properties of septate junctions in Malpighian tubules of Rhodnius
H B Skaer1, S H Maddrell, J B Harrison
1Agricultural and Food Research Council Unit of Insect Neurophysiology & Pharmacology, Department of Zoology, Cambridge, UK.
Abstract:
This paper describes the structural characteristics and permeability properties of the smooth septate junctions between the upper Malpighian tubule cells of a blood-sucking bug, Rhodnius prolixus. The permeability of the paracellular route was tested only for solutes that could be demonstrated not to cross the epithelium via the cellular route. The intercellular clefts were readily permeated by sucrose, inulin and polyethylene glycol (PEG), showing a higher permeability to molecules of smaller radius (PEG versus sucrose). Negatively charged molecules permeated the clefts more readily than positively charged ones. The effects of pH, urea and luminal flow rate on permeability were studied. The results are discussed in relation to the physiological tightness of the Malpighian tubules to certain solutes and to its function as an excretory epithelium.
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