Fig. 5.

Whole-cell currents elicited by nicotine application in undifferentiated PC12 cells. A, The current is shown in response to rapid application of 50 μm nicotine, which was applied at thearrow and continued for 10 sec. The cell was voltage-clamped at a holding potential of −80 mV. B, The current response to 50 μm nicotine before and after application of 500 nm Bgt for 12 min is shown. Nicotine was applied for 200 msec in each trace. C, The fraction of peak current, elicited by nicotine, is plotted, which remains after application of 500 nm Bgt for 10–20 min. On average, the peak current was reduced to 8.8 ± 1.2% of the current measured in the absence of Bgt (Control) for 5 cells.D, The fraction of peak current that remains after application of 500 nm Bgt as a function of time is plotted. Currents were normalized in amplitude to the first application of nicotine (inset currents). The dotted line represents the fit of a single exponential function to the data with a time constant of 5 min. E, The current response to 50 μm nicotine before and after application of 1 μm MLA for 5 min is shown. Nicotine was applied for 200 msec in each trace. There was partial recovery of the current response after 7 min of wash. F, The fraction of peak current that remains after application of 1 μm MLA for 5 to 7 min is plotted. The peak current was reduced to 12.3 ± 1.1% of the current measured in the absence of MLA (Control) for four cells. The peak current reverses to 30.8% of the control current after 7–10 min of wash after the MLA application.