The effect of changing A- and h-type channel conductances on the current-voltage relationship.

(A) The left upper panel shows a plot of A-type current against membrane potential over 4 seconds of firing (I-V loop). This relationship was plotted at different A-type channel maximal specific conductances (

G‾

A

) and in the presence or absence of a tonic, depolarizing, driving current.

G‾

A

and driving current values are given above the plot. The left middle panel shows histograms of the percentage time (% time) the membrane spent at various potentials over the 4 seconds of firing, for two

G‾

A

values. Firing rates were matched by changing the driving input magnitudes in order to separate the effects of changing

G‾

A

(what we were interested in), from the confounding effects of changes in firing rate as a result of changing

G‾

A

. The

G‾

A

and driving current values for the histograms are given to the right of the plot. The lower left panel shows the voltages at which the channels were active (y axis: m_∞ × h_∞ / τ_m × τ_h). The right panel shows action potential and inter-spike interval (upper) and current (lower) traces for the same

G‾

A

/ driving current combinations shown in the histograms. (B) The same as panel A for the hyperpolarization-activated inward (h-type) channel, I_h.