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First published online September 15, 2004
Journal of Experimental Biology 207, iii (2004)
Copyright © 2004 The Company of Biologists Limited
doi: 10.1242/jeb.01271

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Inside JEB

PROCESSING A LIQUID LUNCH

Kathryn Phillips

kathryn{at}biologists.com

Rhodnius prolixus doesn't dine often, but when it does, it really goes to town. Consuming fresh blood meals in excess of ten times its unfed mass, the insects really gorge. But their extravagant tastes come at an enormous metabolic cost; the insect must rid itself of huge volumes of fluid before benefiting from its diet. To counteract the dilute meal, Mike O'Donnell explains that Rhodnius produces hyposmotic urine by secreting sodium, potassium and chloride ions into the Malpighian tubule through a cotransporter. Apparently most cotransporters in this class only function if all three ions are present. But O'Donnell adds that Rhodnius reabsorbs most of the valuable potassium ions further along the Malpighian tubule, and the Rhodnius cotransporter appears to function even when potassium is absent. Puzzled, O'Donnell, Juan Ianowski and Robert Christensen were curious to resolve the apparent contradiction (p. 3707).

Measuring the tubule's secretion rates in the presence of potassium while they raised the sodium levels, the team found that potassium transport became inhibited as the sodium levels rose; sodium transport was replacing potassium transport. So instead of continually losing potassium, the insect retained the precious ion while increasing its sodium and chloride losses. The team suspect that this unusual cotransporter behaviour allows Rhodnius to produce large volumes of dilute salty urine, while retaining potassium, as it processes a liquid lunch.

References

Ianowski, J. P., Christensen, R. J. and O'Donnell, M. J. (2004). Na⁺ competes with K⁺ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus.J. Exp. Biol. 207,3707 -3716.[Abstract/Free Full Text]

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Related articles in JEB:

Na⁺ competes with K⁺ in bumetanide-sensitive transport by Malpighian tubules of Rhodnius prolixus

Juan P. Ianowski, Robert J. Christensen, and Michael J. O'Donnell
JEB 2004 207: 3707-3716. [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Phillips, K. Search for Related Content PubMed Articles by Phillips, K. Social Bookmarking                         What's this?