Transport mechanisms for NaCl in intestinal brush border membrane vesicles (BBMV) of herbivorous, seawater-adapted tilapia, Oreochromis mossambicus, were investigated with a rapid filtration technique using 22Na+ and 36Cl- as tracers. Evidence to support the existence of cotransport mechanisms (Na+/Cl- or Na+/K+/2Cl-) in tilapia intestinal BBMV was not found. An inwardly directed Cl- gradient or KCl gradient did not stimulate the uptake of Na+ into tilapia intestinal BBMV. Furthermore, the uptake of Na+ under these conditions was not significantly affected by furosemide. Evidence was found to indicate the existence of Na+/H+ and Cl-/HCO3- antiport mechanisms for NaCl transport in tilapia intestinal BBMV. An outwardly directed proton gradient (pH 6.0 in, pH 7.5 out) stimulated the uptake of Na+ above that of the control (pH 7.5 in, pH 7.5 out). Exogenous amiloride (1 mmol l-1) significantly reduced Na+ uptake in the presence of an outwardly directed proton gradient. Apparent influxes of 1 mmol l-1 Na+ were (nmol mg protein −1 15 s-1 +/− 1 S.E.): control, 1.46 +/− 0.09; pH gradient, 3.36 +/− 0.14; pH gradient plus amiloride, 1.55 +/− 0.05. The uptake of Cl- was stimulated by outwardly directed HCO3- and Cl- gradients in comparison with an outwardly directed gluconate gradient. Apparent influxes of 10 mmol l-1 Cl- were (nmol mg protein-1 15 s-1 +/− 1 S.E.): gluconate, 12.90 +/− 0.19; HCO3-, 15.83 +/− 0.34; Cl-, 14.62 +/− 0.42. These results suggest that, in contrast to the cotransport mechanisms for NaCl that have been reported for other fish intestine, the herbivorous marine teleost, Oreochromis mossambicus, possesses dual antiport mechanisms for the transport of NaCl across its intestinal brush border membrane.
In the field: an interview with Sönke Johnsen
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Sönke Johnsen is a Professor at Duke University, USA, investigating visual ecology and he talks about his experiences of collecting transparent animals while blue water diving and in a submersible, as well as outrunning Hurricane Katrina.
Call for new preLighters
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preLights is the preprint highlighting community supported by The Company of Biologists. At the heart of preLights are our preLighters: early-career researchers who select and write about interesting new preprints for the research community. We are currently looking for new preLighters to join our team. Find out more and apply here.
Graham Scott in conversation with Big Biology
Graham Scott talks to Big Biology about the oxygen cascade in mice living on mountaintops, extreme environments for such small organisms. In this JEB-sponsored episode, they discuss the concept of symmorphosis and the evolution of the oxygen cascade.
Trap-jaw ants coordinate tendon and exoskeleton for perfect mandible arc
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Trap-jaw ants run the risk of tearing themselves apart when they fire off their mandibles, but Greg Sutton & co have discovered that the ants simultaneously push and pull the mandibles using energy stored in a head tendon and their exoskeleton to drive the jaws in a perfect arc.
Hearing without a tympanic ear
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In their Review, Grace Capshaw, Jakob Christensen-Dalsgaard and Catherine Carr explore the mechanisms of hearing in extant atympanate vertebrates and the implications for the early evolution of tympanate hearing.
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