Intracellular recordings in the hippocampal slice preparation were made with electrodes filled with 0.2 molar potassium EGTA. The purpose was to investigate the role of calcium in mediating afterhyperpolarizations following bursts evoked by intracellular current pulses, arising spontaneously, or induced by the epileptogenic agent penicillin. In the first two cases the afterhyperpolarization was blocked and the associated conductance increase was reduced, suggesting that EGTA was blocking the calcium-activated potassium conductance during the hyperpolarization. In the third case the afterhyperpolarization and associated conductance increase persisted, implicating an alternative mechanism for the hyperpolarization.
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