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First published online January 16, 2009
Journal of Experimental Biology 212, 446-451 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.025916
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Insect homeostasis: past and future

Simon Maddrell

Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK


Figure 1
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  		Fig. 1. Proposed relationship between concentration of hormones and responses of the midgut and Malpighian tubules in fed Rhodnius.

 

Figure 2
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  		Fig. 2. Diuresis in fed 5th stage Rhodnius with one, two or three Malpighian tubules removed.

 

Figure 3
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  		Fig. 3. Proposed relationship between the concentration of hormones and the responses of the midgut and Malpighian tubules in fed Rhodnius with one, two or three Malpighian tubules removed.

 

Figure 4
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  		Fig. 4. A part of a Malpighian tubule from a 5th stage Rhodnius in which a developmental error has led to a cell (arrow) typical of the upper Malpighian tubule coming to lie in a background of lower Malpighian tubule cells. tr, a short length of trachea (air supply system) attached to one of the upper cells. Upper tubule ~70–80 µm in diameter. [From Maddrell and Overton (Maddrell and Overton, 1985Go).]

 

Figure 5
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  		Fig. 5. Diagram of the experimental arrangement used to follow the transporting activity of single upper Malpighian tubule cells. Most of the upper, fluid-secreting region of the Malpighian tubule is placed in a 100 µl drop (A), held in position in a depression in the wax base. This drop contains 10–7 mol l–1 serotonin (5-HT) to stimulate fluid secretion by the upper Malpighian tubule. The lower Malpighian tubule is arranged so that the boundary between it and the upper Malpighian tubule is a short distance upstream from a 20 µl test drop (B). This allows the single upper cell, whose activity is being investigated, to be situated just within the test drop. The test drop contains the radioactive marker being used. Fluid passing down the lumen is collected from a cut in the wall of the Malpighian tubule at (C). The lower drawing shows, in close-up, the upper/lower Malpighian tubule boundary and the position of the single upper cell [from Maddrell and Overton (Maddrell and Overton, 1985Go)].

 

Figure 6
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  		Fig. 6. The transport of radioactive 22Na+ from a test droplet containing a single upper Malpighian tubule cell (upper panel) or where the test droplet does not contain an upper Malpighian tubule cell (lower panel). In each case, 10–7 mol l–1 serotonin (5-HT) was added at 30 min (the first vertical line) and the test droplet was replaced with a droplet of 5-HT-free saline at 90 min (second vertical line) [from Maddrell and Overton (Maddrell and Overton, 1985Go)].

 

Figure 7
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  		Fig. 7. Oscillations in transepithelial potential difference (TEP) measured in an upper Malpighian tubule from a 5th stage Rhodnius in a 100 µl droplet containing serotonin (5-HT) at 10–7 mol l–1. The TEP was steady at approximately –30 mV at the start but started to rise and changed to oscillations of approximately 20 mV after 20 min. The wavelength of the oscillations here was approximately 3 min at the bath temperature of 24°C.

 

Figure 8
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  		Fig. 8. The relationship between bath temperature and wavelength of oscillations in transepithelial potential difference (TEP) in Malpighian tubules from 5th stage Rhodnius stimulated with 10–7 mol l–1 serotonin (5-HT). A wavelength of 2 min has a ln wavelength of 0.69 and a wavelength of 4 min has a ln wavelength of 1.38.

 

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© The Company of Biologists Ltd 2009