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First published online December 22, 2003
Journal of Experimental Biology 207, 519-526 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00772

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Effects of leucokinin-VIII on Aedes Malpighian tubule segments lacking stellate cells

Ming-Jiun Yu and Klaus W. Beyenbach^*

Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA

View larger version (25K): [in a new window]   Fig. 1. In vitro microperfusion of Malpighian tubules of the yellow fever mosquito, Aedes aegypti. (A) Perfusion of a tubule segment containing a stellate cell. (B) Perfusion of a tubule segment without stellate cells. The lumen of Malpighian tubules was cannulated with a double-barreled glass pipette for perfusion of the tubule lumen and for measurements of the transepithelial voltage (Vt) and resistance (Rt). Vl is the voltage measured at the distal end of the perfused segment. A current (I=50 nA) was injected into the tubule lumen when measurements of Rt were desired. BB, brush border; PC, principal cell; SC, stellate cell; SJ, septate junction. (C) Simple electrical equivalent circuit of transepithelial electrolyte transport across Malpighian tubules. Ec, electromotive force of the active transport pathway; I, intraepithelial current; Rc, transcellular resistance; Rsh, shunt resistance. Rt is the total resistance of Rc and Rsh in parallel.

View larger version (45K): [in a new window]   Fig. 2. Malpighian tubules of the female yellow fever mosquito, Aedes aegypti, examined by light (A,B) and electron (C) microscopy. BB, brush border; C, intracellular concretion; M, mitochondrion; N, nucleus; PC, principal cell; SC, stellate cell; SJ, septate junction. Scale bars, 300 µm (A), 40 µm (B), 2.5 µm (C).

View larger version (48K): [in a new window]   Fig. 3. The electrophysiological effects of leucokinin-VIII (1 µmol l-1) on Aedes Malpighian tubule segments with (A-D) or without (E-H) stellate cells. N, nucleus; PC, principal cell; SC, stellate cell; SJ, septate junction. Values are means ± S.E.M. (N, number of Malpighian tubules). Asterisks indicate significant difference (P<0.05).

View larger version (18K): [in a new window]   Fig. 4. Continuous time course of transepithelial voltage (solid line) and resistance changes measured at intervals (tinted bars) in the presence of leucokinin-VIII in Aedes Malpighian tubules devoid of stellate cells. A representative tubule experiment is shown. The on/off responses were as immediate as the changes in peritubular medium.