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First published online August 18, 2005
Journal of Experimental Biology 208, 3281-3291 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01760

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Mosquito natriuretic peptide identified as a calcitonin-like diuretic hormone in Anopheles gambiae (Giles)

Geoffrey M. Coast^1,*, Christopher S. Garside¹, Simon G. Webster², Kathleen M. Schegg³ and David A. Schooley³

¹ Department of Biology, Birkbeck (University of London), London WC1E 7HX, UK
² School of Biological Sciences, University of North Wales, Gwynedd LL57 2UW, UK
³ Biochemistry Department, University of Nevada, Reno, NV 89557, USA

^* Author for correspondence (e-mail: g.coast{at}bbk.ac.uk)

Accepted 22 June 2005

Mosquito natriuretic peptide (MNP), an uncharacterised peptide from the yellow fever mosquito, Aedes aegypti, acts via cyclic AMP to stimulate secretion of Na⁺-rich urine by opening a Na⁺ conductance in the basolateral membrane of Malpighian tubule principal cells. Corticotropin releasing factor (CRF)-related peptides and calcitonin (CT)-like diuretic peptides use cyclic AMP as a second messenger and were therefore considered likely candidates for MNP. BLAST searches of the genome of the malaria mosquito Anopheles gambiae, gave sequences for the CRF-related peptide Anoga-DH₄₄ and the CT-like peptide Anoga-DH₃₁, which were synthesised and tested for effects on Malpighian tubules from An. gambiae and Ae. aegypti, together with 8-bromo-cyclic AMP.

The cyclic AMP analogue stimulated secretion of Na⁺-rich urine by An. gambiae Malpighian tubules, reproducing the response to MNP in Ae. aegypti. It also depolarised the principal cell basolateral membrane voltage (V_b) while hyperpolarising the transepithelial voltage (V_t) to a similar extent.

Anoga-DH₄₄ and Anoga-DH₃₁ stimulated production of cyclic AMP, but not cyclic GMP, by Malpighian tubules of An. gambiae. Both peptides had diuretic activity, but only Anoga-DH₃₁ had natriuretic activity and stimulated fluid secretion to the same extent as 8-bromo-cyclic AMP. Likewise, Anoga-DH₃₁ reproduced the effects of cyclic AMP on tubule electrophysiology, whereas Anoga-DH₄₄ initially hyperpolarised V_b and depolarised V_t, which is the opposite of the effect of Anoga-DH₃₁.

Anoga-DH₄₄ and Anoga-DH₃₁ were also tested for effects on fluid secretion and ion transport by Ae. aegypti tubules. As in An. gambiae, the CRF-related peptide Anoga-DH₄₄ had a non-specific effect on the transport of Na⁺ and K⁺, whereas the CT-like peptide Anoga-DH₃₁ specifically stimulated transepithelial Na⁺ transport.

We conclude that the CT-like peptide Anoga-DH₃₁ is the previously uncharacterised mosquito natriuretic peptide.

Key words: excretion, Malpighian tubule, diuretic hormone, natriuresis, mosquito, Anopheles gambiae, Aedes aegypti

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