Fig.4. Voltage- and time-dependence of depolarising after potentials. (A) The membrane potential (E_M) of a type 1 cell was held at three different potentials by constant current injection. Constant amplitude and duration hyperpolarizing pulses elicit different membrane potential waveforms, depending on E_M. A sag potential (dashed line) occurs during the pulse and a spike is triggered on pulse termination only at the more depolarised E_M. A DAP (arrowed) follows the action potential. Membrane sag and DAP are thus dependent on E_M. (B) Hyperpolarising pulses of constant duration but differing amplitude were injected into a depolarised type 1 cell. DAP amplitude increases with increased hyperpolarising pulses. (C) Constant amplitude hyperpolarizing current pulses of increasing duration were applied to a type 1 cell. DAP amplitude increase with increased pulse duration. (D) The first spike of a spontaneous burst is succeeded by a DAP (arrow).