Verapamil blocks the afterhyperpolarization but not the spike frequency accommodation of rat CA1 pyramidal cells in vitro.

The effects of prolonged periods (up to 4 h) of perfusion with verapamil (100 microM) or D600 (100 microM) on synaptically and directly evoked responses of rat CA1 pyramidal cells were determined in vitro. The slow depolarization underlying burst generation and the slow afterhyperpolarization following directly evoked repetitive firing were blocked, but spike frequency accommodation was not. There was an increase in threshold for evoking synaptic responses and the amplitude of evoked inhibitory postsynaptic potentials (IPSPs) was decreased slightly. The results suggest that verapamil can partially block voltage dependent Ca influx into CA1 cells and that currents underlying accommodation and the slow afterhyperpolarization (AHP) may differ.