Figure 5. Activity enhances I_M during partial, but not complete, suppression by oxo-M.

Currents recorded from a B neuron where I_M was measured by stepping from a holding potential of −30 mV to −50 mV. Top row shows the effect of activity produced by the 40 s, 5 Hz stimulus template in normal Ringer solution. Notice the increases in holding current and in the amplitudes of the slow current relaxations that reflect M channel gating. After the activity-induced increase in I_M subsided (middle row), 1 μm oxo-M inhibited I_M by about 50% and the 40 s stimulus template increased I_M beyond control levels. After washing out oxo-M and allowing the cell to recover from the previous stimulus trial (bottom row), I_M was completely suppressed by 10 μm oxo-M and under these conditions virtual synaptic stimulation failed to restore I_M.