  We investigate calcium signaling feedback through calcium-activated potassium
channels of a dendritic spine by applying the immersed boundary method with
electrodiffusion. We simulate the stochastic gating of such ion channels and
the resulting spatial distribution of concentration, current, and membrane
voltage within the dendritic spine. In this simulation, the permeability to
ionic flow across the membrane is regulated by the amplitude of chemical
potential barriers. With spatially localized ion channels, chemical potential
barriers are locally and stochastically regulated. This regulation represents
the ion channel gating with multiple subunits, the open and closed states
governed by a continuous-time Markov process. The model simulation
recapitulates an inhibitory action on voltage-sensitive calcium channels by the
calcium-activated potassium channels in a stochastic manner as a
\emph{non-local} feedback loop. The model predicts amplified calcium influx
with more closely placed channel complexes, proposing a potential mechanism of
differential calcium handling by channel distributions. This work provides a
foundation for future computer simulation studies of dendritic spine motility
and structural plasticity.
