Multiple Mechanisms for the Potentiation of AMPA Receptor-Mediated Transmission by alpha -Ca2+/Calmodulin-Dependent Protein Kinase II

Some forms of activity-dependent synaptic potentiation require the activation of postsynaptic Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). Activation of CaMKII has been shown to phosphorylate the glutamate receptor 1 subunit of the AMPA receptor (AMPAR), thereby affecting some of the properties of the receptor. Here, a recombinant, constitutively active form of alphaCaMKII tagged with the fluorescent marker green fluorescent protein (GFP) [alphaCaMKII(1-290)-enhanced GFP (EGFP)] was expressed in CA1 pyramidal neurons from hippocampal slices. The changes in glutamatergic transmission onto these cells were analyzed. AMPA but not NMDA receptor-mediated EPSCs were specifically potentiated in infected compared with nearby noninfected neurons. This potentiation was associated with a reduction in the proportion of synapses devoid of AMPARs. In addition, expression of alphaCaMKII(1-290)-EGFP increased the quantal size of AMPAR-mediated responses. This effect reflected, at least in part, an increased unitary conductance of the channels underlying the EPSCs. These results reveal that several key features of long-term potentiation of hippocampal glutamatergic synapses are reproduced by the sole activity of alphaCaMKII.