Hormone-controlled cAMP-mediated fluid secretion in yellow-fever mosquito

Abstract

Evidence is presented for hormone-controlled adenosine 3',5'-cyclic monophosphate (cAMP)-mediated NaCl diuresis in Malpighian tubules of the blood-feeding yellow-fever mosquito Aedes aegypti. Studies in isolated Malpighian tubules reveal that cAMP added to the peritubular bath selectively stimulates NaCl secretion and not KCl secretion by increasing the Na conductance of the basolateral membrane of primary cells. These effects are duplicated by forskolin and theophylline in parallel with increased intracellular concentrations of endogenous cAMP. Two natriuretic peptides that we have isolated by high-pressure liquid chromatography (HPLC) methods from mosquito heads also increase NaCl and fluid secretion in isolated Malpighian tubules together with increased intracellular levels of cAMP. These results are consistent with a mechanism of NaCl diuresis in which the natriuretic peptides and cAMP are respectively the primary and secondary messengers that couple the ingestion of a blood meal to the excretion of the unwanted salt and water fraction of the meal. This hypothesis is supported by in vivo studies that reveal elevated intracellular cAMP levels in Malpighian tubules at the time of maximum NaCl diuresis.

Protein kinase A dependent and independent activation of the V-ATPase in Malpighian tubules ofAedes aegypti.

“…Since blood meal-induced diuresis is known to involve elevation of the intracellular cAMP level (Petzel et al, 1987), we analysed the effect of membranepermeant cAMP analogues on the V-ATPase activity. To exclude the variability in the data from different mosquitoes, tubules from only one mosquito were studied in any one test.…”

“…To test whether Anoga-DH 31 , like MNP (Petzel et al, 1987), increases the intracellular cAMP concentration in A. aegypti Malpighian tubules, we first measured cAMP in 12 unstimulated tubules and found a value of 14pmolmg -1 protein, corresponding to ~11fmol per tubule (Fig.2). Incubating Malpighian tubules with 1μmoll -1 Anoga-DH 31 for 2min significantly increased the intracellular cAMP concentration tenfold to 140pmolmg -1 protein.…”

“…The natriuretic peptide, previously referred to as mosquito natriuretic peptide (MNP) (Petzel et al, 1985) and now known to be the calcitonin-like peptide Anoga-DH 31 , increases the secretion of NaCl-rich fluid in isolated tubules of A. aegypti severalfold (Petzel et al, 1985;Coast et al, 2005). MNP acts via the second messenger cyclic AMP, and its diuretic effects can be duplicated by membrane-permeant cAMP analogues (Petzel et al, 1987;Coast et al, 2005;Beyenbach et al, 2009). In bloodfed mosquitoes an elevated level of MNP was found in the haemolymph, along with an increased cAMP concentration in the Malpighian tubules (Petzel et al, 1987;Wheelock et al, 1988).…”

“…MNP acts via the second messenger cyclic AMP, and its diuretic effects can be duplicated by membrane-permeant cAMP analogues (Petzel et al, 1987;Coast et al, 2005;Beyenbach et al, 2009). In bloodfed mosquitoes an elevated level of MNP was found in the haemolymph, along with an increased cAMP concentration in the Malpighian tubules (Petzel et al, 1987;Wheelock et al, 1988). In contrast to the selective activation of transepithelial Na + secretion by MNP, kinin diuretic peptides selectively activate the transepithelial secretion of Cl -, thereby increasing the transepithelial secretion of NaCl, KCl and water (Pannabecker et al, 1993;Schepel et al, 2010).…”

Mechanisms of K+ transport across basolateral membranes of principal cells in Malpighian tubules of the yellow fever mosquito,Aedes aegypti

“…In Aedes Malpighian tubules, corticotropin-releasing factor (CRF)-like diuretic peptides and their second messenger cAMP selectively increase transepithelial NaCl secretion by activating an Na + conductance in the basolateral membrane of principal cells (Beyenbach, 2001;Petzel et al, 1985Petzel et al, , 1987Beyenbach, 1983, 1984). How the blockade of the Na + /K + /2Cl -cotransporter brings about the blockade of Na + channels is unclear at present.…”