Red cell spectrin phosphorylation and cytoskeletal anchorage.

A cAMP-dependent phosphorylation of spectrin occurred in intact human red blood cells supplemented with cAMP. A cAMP-dependent phosphorylation of spectrin altered its binding properties. Spectrin was resistant to low ionic strength extraction and remained associated with inside-out vesicles (IOV). A cAMP-dependent phosphoform of spectrin contained label in both subunits, when generated in vitro. In vivo, the labeling of spectrin band 1 increased with red cell age. The low extent of spectrin band 1 phosphorylation in young cells could be due to a Ca2+-calmodulin-spectrin interaction, because Ca2+-calmodulin selectively inhibited a cAMP-dependent labeling of spectrin band 1, when tested on purified spectrin dimer.