Potentiation of Ca²⁺ influx through NMDA channels by action potentials: A computer model

IN pyramidal cells, somatic action potentials can propagate actively back into the apical dendrites and potentiate calcium influx at simultaneously activated glutamatergic synapses, presumably by relieving the voltage-dependent block of NMDA channels. We have used computer simulations to investigate the conditions under which this potentiation will be optimal. We find that a spike with a long duration and limited amplitude (peak of ~- 10mV) will be most effective. A backpropagating action potential will achieve this form if the dendritic membrane has a low K⁺ channel density and a modest Na⁺ channel density (30-70pS/μm², similar to experimentally observed densities). The relative increase in calcium due to the backpropagating spike will be small, however, unless the accumulated calcium is rapidly removed.