Figure 1. Bi-exponential neuronal nicotinic voltage-jump relaxation currents.
A–C, the upper traces are the command potential protocols and the lower traces are the voltage-clamped currents. We used a 75 ms prepulse from -50 mV (holding potential) to +50 mV to increase the relaxation amplitudes. Following the pre-pulse, 10 voltage jumps (2.4 s long) were made from +50 mV to a potential between -60 and -150 mV in 10 mV increments. After these jumps, the voltage returned to the holding potential. A, α3β4 voltage-jump currents in the absence of ACh. B,α3β4 relaxation currents in 1 μM ACh. C, difference of currents in A and B. D, fits of the α3β4 ACh-induced difference current at -150 mV to the sum of one (dashed line) or two (continuous line) negative exponentials and a constant. The fit to two exponential components and a constant superimposes on the data. For the two-exponential fit, the fast (τf) and slow (τs) time constants were 96 and 343 ms, respectively. The amplitudes of the fast (If), slow (Is) and steady-state (Iss) relaxation components were 6.8, 5.7 and -14.6 μA, respectively. The fractional amplitude of the fast component (If/Itot) was 0.54. The time constant, relaxation amplitude and steady-state current for the single-exponential fit were 218 ms, 11.0 μA and -14.5 μA, respectively. (See Methods for acquisition filter frequencies and sampling rates.)