Figure 5.

PDP of GABA current was time- and voltage-dependent. A: Current responses to GABA (1 µM) with step depolarizations of increasing duration. Duration of initial depolarization was 1 s and increased by 0.5 s with each subsequent trial (not all traces shown, illustrated traces are for 0, 1.5, 2.5, 3.5, and 4.5 s of depolarization). A progressive increase in current amplitude was seen upon repolarization as the duration of the preceding depolarization increased. Lower panel shows command potentials. Note that the current after 2.5 s of depolarization was larger than the peak current produced by GABA alone. B: Mean potentiation of current as a function of depolarization duration. Current was measured 1.5 s after repolarization and normalized to current values at corresponding time point of control trace (−60 mV) from experiments as in panel A (n=4). C: GABA-evoked currents (3 µM) with step depolarization to a range of potentials from −30 to +30 mV. Current at −60 mV was potentiated by transient depolarization to −30 mV (compared to control current recorded at −60 mV) and increased progressively as the magnitude of the preceding depolarization increased. D: Data from panel C on expanded time scale illustrating the current increase seen upon repolarization. Labels refer to value of preceding depolarization (−60 mV is control). E: Mean normalized current at −60 mV as a function of prepulse potential. Current was measured 1.5 s after repolarization and normalized to corresponding time point of control trace (n=4). Data from experiments as in panel C. Solid line represents a Boltzmann equation fit to the data; the apparent half-maximal voltage (V_0.5) for PDP of GABA current was +10 mV.