Rearrangement of erythrocyte band 3 molecules and reversible formation of osmotic holes under hypotonic conditions

Abstract

The complex phenomenon of rearrangement of band 3 molecules after erythrocyte swelling under hypotonic condition is considered. The rearrangement includes the increase of the mobile fraction and clustering of band 3. The self-associative tendency and the action of the elastic field generated within the lipid membrane after erythrocyte swelling result in equilibration of the number of molecules per cluster and the number of clusters. The local perturbation of the elastic field induces excitation of the cluster in the nearest neighbor and changes its packing state generating changes in the free volume within the cluster. The local perturbation could result in the reversible formation of osmotic hole. We formulated a model to predict changes of the cluster packing states generated by rearrangement of band 3 molecules on two time-scales. The phenomenon is examined on the basis of two experimental sets, i.e. low (5.2 mM Na3PO4 solution) and high (46.0 mM Na3PO4 solution) hypotonicities at 21A degrees C, from Golan and Veatch (Proc Natl Acad Sci 77(5):2537-2541, 1980). Modeling considerations suggested that lower hypotonic conditions resulted in higher values of: the driving force of agglomeration of band 3 as a measure of self-associative tendency, the specific rate of cluster breaking, the specific rate of increase of the mobile fraction of band 3, and the dispersion of cluster sizes. Lower hypotonic conditions ensure the generation of a higher average value of the free energy within the membrane after erythrocyte swelling, which enables more intensive rearrangement of band 3 molecules.