The kinin receptor is expressed in the Malpighian tubule stellate cells in the mosquito Aedes aegypti (L.): A new model needed to explain ion transport?

It is known that insect kinins increase diuresis and fluid secretion in the Aedes aegypti Malpighian tubule, causing a rapid drop of the transepithelial resistance and increasing chloride conductance from the hemolymph towards the tubule lumen. The tubule is composed of both principal and stellate cells. The main route for increased chloride influx upon kinin treatment is proposed to be paracellular, with septate junctions acquiring increased chloride selectivity and conductance. Therefore, kinin treatment renders the Ae. aegypti tubule a “leaky epithelium”, and under this model the kinin receptor is postulated to be expressed in principal cells. However, in another dipteran, the fruit fly Drosophila melanogaster, the main route for chloride transport is transcellular through stellate cells. In both the fruit fly and the mosquito Anopheles stephensi the kinin receptor has been immunolocalized in stellate cells, where it regulates transepithelial chloride permeability. Here we show that in Ae. aegypti, similarly, the stellate cells express the kinin receptor. This was confirmed through immunohistochemistry with two specific anti-kinin receptor antibodies and confocal analysis. The receptor is detected as a 75 kDa band in western blot. These results indicate that the currently accepted model for chloride transport must be re-evaluated in Ae. aegypti and suggest the kinin regulatory signals controlling intercellular junctions originate in the stellate cells.

We provide evidence that the kinin receptor (AY596453) is expressed only in stellate cells in Malpighian (renal) tubules of females of the mosquito Aedes aegypti.Figure optionsDownload high-quality image (170 K)Download as PowerPoint slideResearch highlights
► The Aedes kinin receptor, a GPCR for the three Aedes kinins, is expressed in the basolateral membrane of stellate cells in the mosquito Aedes aegypti Malpighian (renal) tubule as demonstrated by confocal microscopy and immunohistochemistry with two-specific anti-kinin receptor antibodies. This unequivocally demonstrates the protein encoded by AY596453.1 is expressed in the stellate cells and not the principal cells as previously suggested by others.
► There is only one receptor form of 75 kDa (lane 1) in the Malpighian tubule, likely post-translationally modified, because the receptor predicted MW is 65.2 kDa. The existence of only one form expressed in the Malpighian tubule differs from findings in other dipterans, including the mosquito Anopheles stephensi and the fruit fly Drosophila melanogaster in which two forms are present.