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 similar to-10 mV) 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 (30-70 pS/mu m(2), 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. (C):1999 Lippincott Williams & Wilkins.