Control of GluR1 AMPA receptor function by cAMP-dependent protein kinase

Modulation of postsynaptic AMPA receptors in the brain by phosphorylation m ay play a role in the expression of synaptic plasticity at central excitato ry synapses. It is known from biochemical studies that GluR1 AMPA receptor subunits can be phosphorylated within their C terminal by cAMP-dependent pr otein kinase A (PKA), which is colocalized with the phosphatase calcineurin (i.e., phosphatase 2B). We have examined the effect of PKA and calcineurin on the time course, peak open probability (P-O,P-PEAK), and single-channel properties of glutamate-evoked responses for neuronal AMPA receptors and h omomeric GluR1(flip) receptors recorded in outside-out patches. Inclusion o f purified catalytic subunit C alpha-PKA in the pipette solution increased neuronal AMPA receptor P-O,P-PEAK (0.92) compared with recordings made with calcineurin included in the pipette (P-O,P-PEAK 0.39). Similarly, C alpha- PKA increased P-O,P-PEAK for recombinant GluR1 receptors (0.78) compared wi th patches excised from cells cotransfected with a cDNA encoding the PKA pe ptide inhibitor PKI (P-O,P-PEAK 0.50) or patches with calcineurin included in the pipette (P-O,P-PEAK 0.42). Neither PKA nor calcineurin altered the a mplitude of single-channel subconductance levels, weighted mean unitary cur rent, mean channel open period, burst length, or macroscopic response wavef orm for recombinant GluR1 receptors. Substitution of an amino acid at the P KA phosphorylation site (S845A) on GluR1 eliminated the PKA-induced increas e in P-O,P-PEAK, whereas the mutation of a Ca2+, calmodulin-dependent kinas e II and PKC phosphorylation site (S831A) was without effect. These results suggest that AMPA receptor peak response open probability can be increased by PKA through phosphorylation of GluR1 Ser845.