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First published online July 2, 2004
Journal of Experimental Biology 207, 2877-2888 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01102

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The mechanism of action of the antidiuretic peptide Tenmo ADFa in Malpighian tubules of Aedes aegypti

Richard C. Massaro¹, Lenora W. Lee¹, Ankit B. Patel¹, Daniel S. Wu¹, Ming-Jiun Yu¹, Brett N. Scott¹, David A. Schooley², Kathleen M. Schegg² and Klaus W. Beyenbach^1,*

¹ Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA
² Department of Biochemistry, University of Nevada, Reno, NV 89557, USA

View larger version (16K): [in a new window]   Fig. 1. Effects of Tenebrio molitor antidiuretic factor `a' (Tenmo ADFa, 10–9 mol l–1) on transepithelial fluid secretion (A), concentrations of Na+, K+, and Cl– in secreted fluid (B), and transepithelial rates of Na+, K+ and Cl– secretion (C) in isolated Malpighian tubules of A. aegypti. Values are means ± S.E.M. (N=9); *P<0.05, paired Student's t-test.

View larger version (10K): [in a new window]   Fig. 2. Effects of Tenmo ADFa (10–9 mol l–1) on the transepithelial voltage Vt (A) and resistance Rt (B) in isolated perfused Malpighian tubules and on the basolateral membrane voltage Vbl (C) and input resistance Rpc (D) of principal cells of Malpighian tubules of A. aegypti. Values are means ± S.E.M. (N=7).

View larger version (16K): [in a new window]   Fig. 3. Effects of 500 µmol l–1 cyclic guanosine monophosphate (cGMP) on transepithelial fluid secretion (A), on the concentrations of Na+, K+ and Cl– in secreted fluid (B), and on transepithelial rates of Na+, K+ and Cl– secretion in isolated Malpighian tubules of A. aegypti (C). Values are means ± S.E.M.; N=24 tubules (A), N=12 tubules (B,C); *P<0.05, paired Student's t-test.

View larger version (10K): [in a new window]   Fig. 4. Effects of cGMP (500 µmol l–1) on the transepithelial voltage Vt (A) and resistance Rt (B) in isolated perfused Malpighian tubules and on the basolateral membrane voltage Vbl (C) and input resistance Rpc (D) of principal cells of Malpighian tubules of A. aegypti. Values are means ± S.E.M.; N=20 (A–C), N=21 (D) tubules or cells; *P<0.05, paired Student's t-test.

View larger version (21K): [in a new window]   Fig. 5. Dose–response of the effects of cGMP on the basolateral membrane voltage Vbl (A), and the input resistance Rpc (B) of principal cells in isolated Malpighian tubules of A. aegypti. The insert in A illustrates the usual biphasic response of Vbl to 500 µmol l–1 cGMP. Values are means ± S.E.M.; the number of principal cells is indicated for each data point; *P<0.05, paired Student's t-test. Open circles, steady state depolarization; closed circles, peak depolarisation.

View larger version (40K): [in a new window]   Fig. 6. Model of transepithelial electrolyte and fluid secretion in isolated Malpighian tubules of A. aegypti. The tubule consists of principal and stellate cells in a ratio of 5:1 (Beyenbach, 2003). Transepithelial secretion of Na+ and K+ is transcellular, and secretion of Cl– is paracellular and/or through stellate cells under control conditions. The transepithelial Cl– flux is largely paracellular through septate junctions under diuretic conditions stimulated by leucokinin (Yu and Beyenbach, 2004). The V-type H+-ATPase located at the apical membrane powers transcellular and paracellular transport via electrical coupling (Beyenbach, 2003). The Na/K ATPase may be present in stellate cells, but its contribution to transepithelial electrolyte and fluid secretion appears to be minor or negligible in view of a high V-type H+-ATPase activity and a low Na/K ATPase measured in Aedes Malpighian tubules (Weng et al., 2003). Control data for the Tenmo ADFa experiment of Fig. 1 are shown. The Cl– channel in the basolateral membrane of principal cells is hypothetical to allow the exit of Cl– such that the epithelial cell remains in steady state. Vbl, basolateral membrane voltage; Va, apical membrane voltage; Vt, transepithelial voltage; Rpc, input resistance, principal cell; Rt, transepithelial resistance.