Model of dynamic AQP4 segregation in astrocyte plasma membrane. M1–AQP4 expressed individually redistributes throughout the plasma membrane and is available to diffuse into rapidly extending plasma membrane regions. M23–AQP4 expressed individually does not diffuse rapidly enough to reach protruding membrane areas, but preferentially concentrates at astrocyte end-feet due to increased affinity of large OAPs for end-foot adhesion complexes. Co-expressed M1– and M23–AQP4 form arrays of varying M1/M23 ratio, size, and diffusional mobility in which large, M23-enriched arrays are available for polarization, and small, M1-enriched arrays and single tetramers are available to support extension of peripheral astrocyte processes.