Figure 4.

Calcium currents for both channel types in response to the motor neuron AP waveform. (A) Comparison of a recorded AP waveform from a CaP motor neuron in vivo (red open circles) with the one used to simulate calcium currents with Scheme 1 (solid line). The simulated AP waveform was constructed from 27 voltage ramps concatenated to match the recorded waveform. (Dashed line) 0 mV. (B) Experimentally measured average Ca_V2.2 (n = 8) and Ca_V2.1 (n = 7) calcium currents elicited in response to a neuronal AP. To obtain average values, each recording was normalized to the total available calcium current in that cell by using the peak tail current during a step from +70 mV to −80 mV. (Solid lines) Predicted calcium currents with the GHK permeation regime in response to the simulated AP based on Markov chain simulations using the software IonChannelLab (12). Parameters were based on Scheme 1 and extra- and intracellular Ca²⁺ concentrations were set to 2 mM and 4 μM, respectively, to yield a calcium reversal potential of ∼+80 mV. (Calibration bar) 0.1 normalized calcium current; (dashed traces) 0 current level.