Potassium-induced long-term potentiation in rat hippocampal slices

We observed that a transient increase in extracellular potassium concentration (50 mM for 40 s) was sufficient to induce long-term potentiation (LTP) of synaptic transmission in area CA1 of the hippocampal slice. Potassium-induced potentiation of the Schaffer collateral/commissural synapses demonstrated several features characteristic of tetanus-induced LTP: (1) population excitatory post-synaptic potential (EPSP) amplitudes were enhanced to a similar magnitude (on average 70% above baseline) which (2) lasted for more than 20 min; (3) induction was blocked by bath application of the specific N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovalerate (D-APV), and (4) was attenuated by reduction of the concentration of calcium in the extracellular medium. Induction of either potassium-induced LTP or tetanus-induced LTP occluded the subsequent expression of the other. Finally, exposure to high potassium in the absence of electrical stimulation was sufficient to induce LTP. Taken together, these data indicate that brief depolarizing stimuli other than tetanus can induce LTP. Because potassium-induced LTP is not restricted to the subset of afferents examined electrophysiologically, such a method could facilitate analyses of the biochemical events underlying both the induction and expression of LTP.