A role for protein kinases and phosphatases in the Ca(2+)-induced enhancement of hippocampal AMPA receptor-mediated synaptic responses.

We have investigated the effects of inhibitors of protein kinases and protein phosphatases on the NMDA receptor-independent potentiation of evoked and miniature (m) excitatory postsynaptic currents (EPSCs) induced by the entry of Ca2+ via voltage-gated Ca2+ channels in hippocampal CA1 pyramidal neurons. Voltage pulse-induced potentiation was markedly attenuated when evoked in the presence of the protein kinase blockers KN-62, K-252a, or H-7. Bath application of the protein phosphatase inhibitor calyculin A converted the usual transient potentiation of both evoked and spontaneous EPSCs induced by voltage pulses into a more sustained potentiation. Similarly, the introduction of the phosphatase inhibitors microcystin LR or okadaic acid into postsynaptic cells, via patch pipettes, also resulted in a sustained increase in the amplitude of mEPSCs. We propose that entry of Ca2+ into CA1 neurons activates calcium/calmodulin-dependent protein kinase II, which leads to an enhanced responsiveness of synaptic AMPA receptor channels. The enhancement is transient, however, owing to postsynaptic phosphatase activity.