Fig. 3.
Voltage dependence and TTX block of cation channel activity in excised patches of bag cell neuron membrane. A, Sample steady-state recordings of cation channel activity in an excised inside/out patch held at the potentials indicated above each trace. Downward deflections correspond to inward current. B, Average open-channel current–voltage relation (bottom, •) and voltage-dependence of the Po(top) from seven inside/out patches containing single cation channels. The open circles were obtained from the relation I = i × Poapplied to each data point, where i represents the open-channel current. A Boltzmann function was fit to thePo points using a Simplex fitting routine with the minimax criterion for error minimization (pCLAMP6); other curves were fit to the points by eye. C, TTX block of cation channel activity in an excised outside/out patch held at −60 mV. At the start of the experiment, four current levels were observed, suggesting the presence of four cation channels in the patch. The activity remaining at 80 μm TTX seemed to be attributable predominantly to the presence of a smaller conductance channel, which sometimes was observed in inside/out patches.