Fig. 3.

Effect of 5-methylfurmethiodide (MFI) on membrane potential and conductance. A) Effect of 300 µM MFI in the presence of 6 mM calcium. A 2-min application of MFI produces a 10 mV depolarization and a small change in input conductance (downward pulses) but a clear increase in the anode break spikes was produced at the end of each hyperpolarizing potential response to the injected current pulse. The central trace is the membrane potential, −35 mV; the downward deflection is the voltage response to injected current. The resting input conductance was 2.4 µS; and the upward deflection is the anode break spike that followed the end of the 40 nA hyperpolarizing current pulse. There was a slow 13 mV depolarization associated with a very small conductance increase of 0.1 µS; the response took 75 s form onset to reach its peak. The anode break spikes increased in amplitude during MFI application from 11 mV to 17 mV. B) Lower time-resolution recording of a representative recording of applying increasing concentrations of MFI on the membrane potential and resting conductance of the muscle cell. There was little effect at 10 µM MFI but a noticeable effect at 30 µM MFI; again there was a very slow onset and offset of the response. C) Representative recordings of the effect of acetylcholine (ACh) on membrane potential. Note that the time course is faster than that of MFI. The faster time-course (onset and offset) of the depolarizing response to 3 µM acetylcholine with the peak occurring with our application method within 9 s after onset.