Coupling of agonist-induced AMPA receptor internalization with receptor recycling

Excitatory post-synaptic currents in the CNS are primarily mediated by alph a -amino-3-hydroxy-5-methyl-isoxazole-4nic acid (AMPA) receptors in respons e to glutamate. internalization of cell-surface receptors has been shown to be one mechanism by which to control receptor function. To test for agonis t control of AMPA receptor plasma membrane expression we used biochemical a ssays to study AMPA receptor internalization and insertion processes. in he terologous cells, we observed a slow constitutive internalization and a rap id agonist-induced internalization of AMPA receptors. To our surprise, howe ver, agonist treatment had no effect on the steady-state levels of AMPA rec eptors on the cell surface. To examine whether this could be explained by a n agonist-induced increase in the insertion rate of AMPA receptors into the plasma membrane we developed an assay to independently measure receptor in sertion. Remarkably, agonist treatment of cells also dramatically increased AMPA receptor plasma membrane insertion rates. In addition, using an assay to measure recycling of internalized pools we found that internalized rece ptors are rapidly recycled to the cell surface. These results suggest that agonist-induced receptor internalization is coupled to increases in recepto r recycling. This increase in receptor flux through intracellular pools may allow for rapid changes in receptor surface expression by independent regu latory control of internalization and insertion.