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Title: The control of epithelial fluid secretion in Malpighian tubules of Drosophila melanogaster
Author: Caldwell, F. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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Drosophila melanogaster Malpighian tubules, the fastest transporting epithelia known to date, are an ideal model for studying regulation of fluid secretion. My main discoveries using Oregon R strain tubules were as follows. I showed that ouabain, an inhibitor of Na+/K+-ATPase had no effect on tubules' fluid secretion. Octopamine, which stimulates tubules of several other insect species, had no stimulatory effect on these tubules. I discovered that Drosophila tubules are sensitive to much lower concentrations of cAMP than any other known insect. I found differential sensitivity of the posterior and anterior tubules to cAMP. Using radioactive labelling experiments, I found the presence of a cotransporter for cAMP and cGMP on the principal cells' membranes. I proved that tubules are sensitive to very low levels of cGMP. Using membrane permeant analogues of cAMP and cGMP, namely 8-Br-cAMP and 8-Br-cGMP, I discovered that there is a cAMP signalling pathway, but no cGMP pathway, within the secondary "stellate" cells of Oregon R Drosophila melanogaster. I proved that Oregon R tubules are sensitive to extremely low concentrations of cardioacceleratory peptide CAP2b. I used the recently discovered naturally occurring Drosophila melanogaster mutants with over expressed cGMP-dependent protein kinase ("Forager R") and under expressed cGMP-dependent protein kinase ("Forager S" and "Forager S2") to analyse regulatory mechanisms of fluid secretion. I found that mutants with under expressed cGMP-dependent protein kinase were, in fact, much more responsive to cGMP, to CAP2b and extremely responsive to cAMP compared with Oregon R tubules. I showed that mutants with over expressed cGMP-dependent protein kinase were less responsive to cGMP, CAP2b and to cAMP than Oregon R tubules. Thus, both the cAMP and cGMP pathways were affected by the mutation regarding expression of cGMP-dependent protein kinase., I speculate that phosphodiesterase may be affected by under expression or over expression of cGMP-dependent protein kinase, thereby actually overcompensating for the naturally occurring mutation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available