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First published online January 17, 2007
Journal of Experimental Biology 210, 541-552 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02681

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Trimethylamine oxide suppresses stress-induced alteration of organic anion transport in choroid plexus

Alice R. A. Villalobos^1,2,* and J. Larry Renfro^1,3

¹ Center for Membrane Toxicological Studies, Mount Desert Island Biological Laboratory, Salisbury Cove, ME 04672, USA
² Environmental Medicine, University of Rochester, Rochester, NY 14642, USA
³ Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA

^* Author for correspondence (e-mail: alice_villalobos{at}urmc.rochester.edu)

Accepted 5 December 2006

The effect of physicochemical stress on organic anion transport across the vertebrate blood–cerebrospinal fluid (CSF) barrier in the presence and absence of an endogenous cytoprotectant, trimethylamine oxide (TMAO), was investigated in isolated IVth choroid plexus (CP) of spiny dogfish shark (Squalus acanthias), an animal with naturally high levels of TMAO (70 mmol l^–1). Active transepithelial absorption of the organic anion, 2,4-dichlorophenoxyacetic acid (2,4-D), by IVth CP mounted in Ussing chambers was measured after in vitro stress, and a marker for the cellular stress response, inducible heat shock protein 70 (Hsp70), was assayed by immunoblot analysis. Transient heat stress (a shift from the normal 13.5°C to 23.5°C for 1 h) decreased 2,4-D transport by 66%; however, the same stress minus TMAO (isosmotic replacement with urea) had no effect on transport rate. In the absence of TMAO, stress-induced Hsp70 accumulation was more than double that seen in the presence of TMAO. Likewise, exposure to 50 µmol l^–1 Zn for 6 h induced a twofold greater Hsp70 accumulation in the absence of TMAO than in its presence, and the higher Hsp70 level was associated with a higher 2,4-D transport rate. Heat stress and 50 µmol l^–1 Zn also induced more pronounced increases in Hsp70 mRNA in the absence of TMAO. Thus, the cellular stress response can significantly alter CP organic anion transport capacity, and an endogenous osmolyte can suppress that response.

Key words: choroid plexus, heat shock response, Hsp70, 2, 4-dichlorophenoxyacetic acid transport, dogfish shark, elasmobranch

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