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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Texas Red transport across rat and dogfish shark (Squalus acanthias) choroid plexus

¹Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Heidelberg, Germany; ²Laboratory of Pharmacology, National Institutes of Health/National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina; and ³Mount Desert Island Biological Laboratory, Salisbury Cove, Maine

Submitted 21 April 2008 ; accepted in final form 20 July 2008

Confocal microscopy and image analysis were used to compare driving forces, specificity, and regulation of transport of the fluorescent organic anion, Texas Red (sulforhodamine 101 free acid; TR), in lateral choroid plexus (CP) isolated from rat and an evolutionarily ancient vertebrate, dogfish shark (Squalus acanthias). CP from both species exhibited concentrative, specific, and metabolism-dependent TR transport from bath to subepithelial/vascular space; at steady state, TR accumulation in vascular/subepithelial space was substantially higher than in epithelial cells. In rat CP, steady-state TR accumulation in subepithelial/vascular spaces was reduced by Na⁺-replacement, but was not affected by a 10-fold increase in buffer K⁺. In shark CP, Na⁺-replacement did not alter TR accumulation in either tissue compartment; subepithelial/vascular space levels of TR were reduced in high-K⁺ medium. In both species, steady-state TR accumulation was not affected by p-aminohippurate or leukotriene C4, suggesting that neither organic anion transporters (SLC22A family) nor multidrug resistance-associated proteins (ABCC family) contributed. In rat CP, digoxin was without effect, indicating that organic anion transporting polypeptide isoform 2 was not involved. Several organic anions reduced cellular and subepithelial/vascular space TR accumulation in both tissues, including estrone sulfate, taurocholate, and the Mrp1 inhibitor MK571. In rat CP, TR accumulation in subepithelial/vascular spaces increased with PKA activation (forskolin), but was not affected by PKC activation (phorbol ester). In shark, neither PKA nor PKC activation specifically affected TR transport. Thus, rat and dogfish shark CP transport TR but do so using different basic mechanisms that respond to different regulatory signals.

organic anion transport; confocal imaging; organic anion transporter; organic anion transporting polypeptide; multidrug resistance-associated protein