Oligomeric forms of skate erythrocyte band 3. Effect of volume expansion.

Volume expansion of little skate (Raja erinacea) erythrocytes leads to the formation of oligomeric forms of the band 3 protein. The oligomers are formed following incubation in hypotonic media or inclusion of a permeant solute such as ethylene glycol. Oligomers were detected by specifically labeling the skate erythrocyte band 3 homolog with the radiolabeled stilbene [3H]4,4'-diisothiocyano-1,2 diphenylethane-2,2'-disulfonic acid and cross-linking membrane proteins with the homobifunctional agent bis(sulfosuccinimidyl) suberate. Under isoosmotic conditions, the distribution of band 3 in the monomer, dimer, and tetramer forms was 38, 54, and 8%. Medium of 0.5 osmolarity caused the distribution to change to 22% monomer, 31% dimer, and 47% tetramer. Upon return to isoosmotic conditions, cell volume, as well as the distribution of band 3 in the monomer, dimer, and tetrameric forms, returned to control values. Return of hypotonically swollen cells to isoosmotic conditions also returned taurine efflux back to control values. Hyperosmolarity caused a 20% shrinkage of cell volume but did not have any effect on either taurine efflux or the distribution of band 3 in the oligomeric forms. Pyridoxal 5'-phosphate and dinitrostilbene disulfonate, two agents that interact with and cause the formation of the tetrameric form of human band 3, also caused a shift toward to tetrameric peak in skate band 3. To determine whether the cross-linked oligomers had proteins that closely associate with band 3 in the intact cell, Western blots were performed to detect ankyrin and band 4.1. Neither protein appeared with the dimeric or tetrameric forms of band 3, suggesting that the mobility shift was in fact due to association of band 3 monomers. This is the first demonstration that oligomerization of band 3 occurs during a physiologic effect that may be mediated by the band 3 protein.