Figure 6.

Plasticity of membrane excitability is dependent upon calcium channels. A, With intracellular blockade of Ca²⁺ channels with Cd²⁺ (depicted here) or Ni²⁺, TBF was not able to cause a decrease of membrane excitability. B, Plotted over time, intracellular application of Cd²⁺ or Ni²⁺ blocked TBF-induced reductions of membrane excitability. C, Even when membrane excitability was measured over a range of current steps to produce a full input–output curve, TBF did not decrease excitability if Ca²⁺ channels were blocked (plotted here is intracellular Cd²⁺; gray line represents the difference between baseline and post-TBF excitability). D, This lack of effectiveness of TBF is not caused by insufficient action potential firing during TBF, as most of the experiments were performed with >2.5 action potentials per burst, and there was still minimal plasticity. E, The effects of TBF on neuronal input resistance were blocked by intracellular blockade of calcium channels with Cd²⁺ or Ni²⁺ (displayed in this figure are examples with Cd²⁺, baseline R_n = 40 MΩ, post-TBF = 42 MΩ; black circle, baseline; gray circle, post-TBF). F, The effects of TBF on membrane time constant were also blocked by intracellular blockade of calcium channels (bottom; baseline, 12.7 ms; post-TBF, 13.1 ms). In almost all control neurons tested (see above), TBF decreased R_n and the time constant, while this effect of TBF was rarely observed if calcium channels were blocked (plotted here with intracellular Cd²⁺).