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Articles in PresS, published online ahead of print January 17, 2002
Am J Physiol Regu Physiol, 10.1152/ajpregu.00677.2001
Submitted on November 12, 2001
Accepted on January 9, 2002
1 Mount Desert Island Biological Laboratory, Salisbury Cove, ME, USA; Environmental Medicine, University of Rochester, Rochester, NY, USA
2 Mount Desert Island Biological Laboratory, Salisbury Cove, ME, USA; LCP, NIH-NIEHS, Research Triangle Park, NC, USA
3 Mount Desert Island Biological Laboratory, Salisbury Cove, ME, USA; Department of Physiology and Neurobiology, University of Connecticut-Storrs, Storrs, CT, USA
* To whom correspondence should be addressed. E-mail: alice_villalobos{at}urmc.rochester.edu.
Spiny dogfish shark (Squalus acanthias) lateral and IVth choroid plexuses (CP) are ultrastructurally similar to the corresponding tissues of rat. However, shark IVth CP is proportinally larger and easily accessible. Moreover, this epithelial sheet can be halved adn studied in Ussing flux chambers. We have characterized transepithelial of the organic anions, fluorescein (FL) and 2,4-dichlorophenoxyacetic acid (2,4-D), by shark CP using confocal fluorescence microscopy and radiotracer techniques, respectively. Lateral and IVth CP accumulated 1µM FL, with levels in teh underlying extracellular spaces > epithelial cells > medium. 2,4-D and probenecid inhibited FL accumulation in cells and extracellular spaces, suggesting these substractes compete for common carriers. Unidirectional absorptive (CSF to blood) and secretory (blood to CSF) fluxes of 10 µM 14C-2,4-D were measured under short-circuited conditions in IVth plexus mounted in Ussing chambers. 2,4-D underwent net absorption wiht an average flux ratio of 7. Probenecid, 2,4,5-trichlorophenoxyactic acid and 5-hydroxyindoacetic acid, reduced net absorption, reversibly inhibiting unidirectional absorption with no effect on secretion. Ouabain irreversibly reduced net 2,4-D absorption and both cellular and extracellular accumulation of FL, suggestion energetic coupling of OA absorption to sodium transport. Collectively, these data indicate that shark CP actively removes OAs from CSF by a process that is specific and active.
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