Modulation of erythrocyte band 4.1 binding by volume expansion

Erythrocyte band 4.1 is an important protein in the control and maintenance of the cytoskeleton. Skate erythrocyte band 3, the anion exchanger, appear s to play a pivotal role in the regulation of volume-stimulated solute effl ux during volume expansion. Because band 4.1 interacts with band 3, we test ed whether their interaction might change during volume expansion. Skate re d blood cells were volume-expanded in either hypotonic media tone-half osmo larity) or were swollen under isoosmotic conditions by inclusion of ethylen e glycol or ammonium chloride in the medium. Microsomal membranes isolated from red cells under volume expanded conditions demonstrated a significant decrease in the amount of band 4.1 bound to band 3. In unstimulated cells, approximately one third of the binding of band 4.1 occurred to band 3. This binding was characterized as being sensitive to competition by the peptide IRRRY. The majority of band 4.1 is bound to glycophorin las demonstrated i n other species), and this binding does not change during volume expansion. The alteration in band 4.1:band 3 interaction occurs within 5 min after vo lume expansion and is transient, returning to near normal interaction withi n 60 min. Two drugs that promote band 3 oligomerization, pyridoxal-5'-phosp hate and DIDS, also decreased band 4.1 interaction with band 3. Band 4.1 an d ankyrin binding to band 3 may be reciprocally related as high-affinity an kyrin binding sites to band 3 observed under volume-expanded conditions are decreased by inclusion of band 4.1 in the binding reactions. (C) 2001 Wile y-Liss,Inc.