ASSOCIATION OF THE BAND-3 PROTEIN WITH A VOLUME-ACTIVATED, ANION AND AMINO-ACID CHANNEL - A MOLECULAR APPROACH

In response to swelling, cells recover their initial volume by releasi ng intracellular solutes via volume-sensitive pathways, There is incre asing evidence that structurally dissimilar organic osmolytes (amino a cids, polyols, methyl amines), which are lost from cells in response t o swelling, share a single pathway having the characteristics of an an ion channel. However, the molecular identity of this pathway remains t o be established, It has been suggested that the erythrocyte anion exc hanger (AE1) or some AE1-related proteins could be involved. A direct evaluation of this possibility has been made by comparing the function al properties of two AE1s when expressed in Xenopus laevis oocytes: tA E1 is from a fish erythrocyte which releases taurine when swollen, and mAE1 is from a mammalian erythrocyte which does not regulate its volu me when swollen. While mAE1 performs exclusively Cl-/Cl(-)exchange, tA E1 behaves as a bifunctional protein with both anion exchange and Cl-/ taurine channel functions, Construction of diverse tAE1/mAE1 chimaeras allows the identification of protein domains associated with this cha nnel activity, Thus, some AE1 isoforms could act as a swelling-activat ed osmolyte channel, a result having a potentially important implicati on in malaria. This review also discusses the possibility that several different proteins might function as swelling-activated osmolyte chan nels.