Fig. 2.
Met-enkephalin-sensitive synaptic activity reverses polarity near the chloride equilibrium potential and is blocked by the GABAA receptor antagonist bicuculline.A, Whole-cell current-clamp recording from a GABA-type MSDB neuron with a K-gluconate-containing patch electrode. Note the fast afterhyperpolarization and the depolarizing sag. Consecutive 0.5 sec traces show spontaneously occurring IPSCs recorded under different experimental conditions. The first sets of traces show IPSCs recorded at −60 mV under control conditions, with met-enkephalin and after washout of met-enkephalin. Subsequent sets of traces show IPSCs recorded under control conditions at different holding potentials (ranging from −60 to −120 mV). Note the changes in amplitude and polarity of the synaptic currents at different holding potentials. Thebar chart summarizes the data shown above. The mean IPSC amplitude under control conditions is plotted against different holding potentials. Note that the mean amplitude of the met-enkephalin-sensitive IPSCs decreased at more negative holding potentials and reversed polarity between −80 and −90 mV, which is close to the calculated ECl- of −80 mV. This experiment was done in presence of 20 μm CNQX and 50 μm AP-5 to block excitatory synaptic currents.B, In this cell, bicuculline blocked the spontaneously occurring IPSCs in a reversible manner. Subsequent sets of traces show the inhibitory effect of met-enkephalin. Note that the μ-selective opioid receptor agonist DAMGO mimicked the effect of met-enkephalin. All drugs were applied consecutively to the same cell.