Fig. 10.

Different action potential repolarization mechanisms in soma and presynaptic axon terminals of CA3 pyramidal cells. A, Action potentials recorded intracellularly from the soma of a CA3 pyramidal cell, before and during bath application of IbTX (60 nm). The toxin slowed the repolarization and blocked the fast afterhyperpolarization (fAHP), indicating that BK channels dominate during most of the spike repolarization. B, Compound action potential recorded extracellularly from presynaptic axon terminals [i.e., fiber volley (FV) in response to stimulation of axons in stratum radiatum of CA1]. In contrast to the soma, the FV was not significantly affected by bath application of IbTX (60–100 nm). Summary data for all recordings are shown in C (n = 4;p = 0.0023) and D(n = 5; p = 0.17). Because the CA3 pyramidal cells give rise the majority of the CA1 stratum radiatum axons studied here, the contrasting results imply that two subcellular compartments within the CA3 pyramid cells use different spike repolarization mechanisms.