Fig. 3.

Properties and somato-dendritic distribution of sodium channels. A, Three consecutive single sweeps of cell-attached patch currents recorded from a stem dendrite. Note the clear appearance of a fast inward current followed by a slower outward current. The bottom trace is an average (n = 30 trials), and the dashed linerepresents a fit to the rising and decaying phase of the outward current (see Materials and Methods). Note that extrapolation of this fit indicates that there is no significant outward current activation at the time of the peak of the inward current. The voltage protocol is shown as an inset. B, Superposed averaged (n = 5 trials) cell-attached current records demonstrate the voltage dependence of activation of the fast inward current; data were obtained from a dendritic primary branch point. Thedashed lines represent fits made to the rise and decay of the outward current. The voltage protocol is shown as aninset. C, Pooled data demonstrating the somato-dendritic distribution of the fast inward (sodium) current during test pulses to +90 mV, as shown in A. Theline is an unconstrained regression fit. Filled squares show mean (±SD) current as a function of distance from the soma (±SD) for recordings made from the soma, stem dendrites, primary branch points. and higher order dendrites (fromleft to right, respectively). Note that for higher order dendrites the amplitude of the fast inward (sodium) current is on average reduced. D, Normalized current–voltage relationship. Families of currents for a single neuron were normalized to the maximal value, and then data from different neurons were pooled (n = 13).