Hypotonic-stimulated taurine efflux in skate erythrocytes: regulation by tyrosine phosphatase activity.
Treatment of skate erythrocytes with FCCP, dinitrophenol, or sodium azide lowers ATP levels and inhibits Na+-independent taurine uptake after hypotonic volume expansion. Inside-out vesicles isolated from hypotonic volume-expanded cells demonstrate greater Na+-independent taurine uptake, and pretreatment of cells with FCCP abolishes this stimulation. Addition of ATP to the vesicles does not restore stimulated taurine uptake, suggesting that ATP does not act as a ligand modulator on the transporter. Therefore the role of protein phosphorylation was investigated. Because known protein kinase inhibitors have previously been found to have little effect on taurine fluxes in skate erythrocytes, we focused on the effects of protein phosphatase inhibition. When volume-expanded cells were returned to isotonic medium, taurine flux returned to basal values more slowly after treatment with the tyrosine phosphatase inhibitor pervanadate, suggesting that dephosphorylation may regulate inactivation. A similar effect of phosphatase inhibitors was observed in the inside-out vesicles from volume-expanded cells: the reversal of stimulated taurine uptake takes place more slowly in vesicles prepared from cells that had been incubated with pervanadate. Band 3, a major protein involved in the taurine transport pathway, shows increased tyrosine phosphorylation after hypotonic volume expansion. Pervanadate treatment of the cells potentiates and prolongs the increased phosphorylation. Therefore tyrosine phosphorylation of band 3 may play an important role in the activation of taurine fluxes after volume expansion.
Musch
M W
MW
Department of Medicine, Inflammatory Bowel Disease Center, University of Chicago, Chicago, Illinois 60637, USA.
Davis-Amaral
E M
EM
Leibowitz
K L
KL
Goldstein
L
L
D000255:Adenosine Triphosphate / Q000172:deficiency; D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D007038:Hypotonic Solutions / Q000494:pharmacology*; D019000:Phosphotyrosine / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D012860:Skates, Fish / Q000097:blood*; D013654:Taurine / Q000037:antagonists & inhibitors / Q000097:blood*; D014638:Vanadates / Q000494:pharmacology
D001457:Anion Exchange Protein 1, Erythrocyte; D004791:Enzyme Inhibitors; D007038:Hypotonic Solutions; C076715:pervanadate; D013654:Taurine; D019000:Phosphotyrosine; D014638:Vanadates; D000255:Adenosine Triphosphate; D017027:Protein Tyrosine Phosphatases