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1 Department of Medicine, The University of Chicago, Chicago, IL, USA; Mount Desert Island Biological Laboratory, Salsbury Cove, ME, USA
2 Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, RI, USA; Mount Desert Island Biological Laboratory, Salsbury Cove, ME, USA
* To whom correspondence should be addressed. E-mail: mmusch{at}medicine.bsd.uchicago.edu.
Upon exposure to hypotonic medium, skate erythrocytes swell and then reduce their volume by releasing organic osmolytes and associated water. The regulatory volume decrease is inhibited by stilbenes and anion exchange inhibitors, suggesting involvement of the erythrocyte anion exchanger skAE1. To determine the role of tyrosine phosphorylation, erythrocytes were volume expanded with and without prior treatment with the tyrosine kinase inhibitor piceatannol. At the concentration used, 130 µM, piceatannol nearly completely inhibits p72syk, a tyrosine kinase previously shown to phosphorylate skAE1 (21). Hyposmotic-induced volume expansion stimulated association of p72syk with a light membrane fraction of skate red blood cells. Piceatannol did not inhibit this association, but decreased hyposmotically-stimulated increased skAE1 tyrosine phophorylation. Movement of skAE1 from an intracellular to a surface detergent resistant membrane domain as well as tetramer formation were not inhibited by piceatannol treatment. Two effects of hyposmotic-induced volume expansion, decreased band 4.1 binding and increased ankyrin, were both inhibited by piceatannol. These results suggest that at least one event requiring p72syk activation is pivotal for hyposmotic-induced increased transport, however, steps which do not require tyrosine phosphorylation may also play a role.
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