Inhibition of volume-stimulated taurine efflux and tyrosine kinase activity in the skate red blood cell

Phosphorylation of the band 3 anion exchange protein by the tyrosine kinases p72syk and p56lyn is thought to play a role in the pathway that regulates swelling-activated taurine efflux from the skate red blood cell. In this study, the protein tyrosine kinase (PTK) inhibitors piceatannol and tyrphostin A23 both inhibited taurine efflux and the activities of the tyrosine kinases p72syk and p56lyn in the skate erythrocyte. However, the PTK inhibitors genistein and tyrphostin A46 had only small effects on taurine efflux and PTK activities. In general, a strong correlation between the extent of inhibition of taurine efflux and of tyrosine kinase activity was observed. PTK inhibitors showed a similar pattern of inhibition of band 3 phosphorylation, with the greatest inhibition observed in cells treated with piceatannol. The protein kinase C inhibitors staurosporine and bisindolylmaleimide tested alone or in combination with piceatannol had little or no significant effect on swelling-activated taurine efflux. Overall the results support the hypothesis that phosphorylation of the skate band 3 protein by p72syk and p56lyn contributes to the regulation of volume-activated taurine efflux in skate red cells, and suggest that protein kinase C may not be involved in this regulation.