D. Boda et al., Monte Carlo simulations of the mechanism for channel selectivity: The competition between volume exclusion and charge neutrality, J PHYS CH B, 104(37), 2000, pp. 8903-8910
A mechanism for selectivity of calcium over sodium in a biological channel
is studied by means of a Monte Carlo simulation. This model channel is an i
nfinite cylinder containing negatively charged glutamates, each modeled as
a pair of half charged oxygens, and an electrolyte. The fluid in the channe
l is in equilibrium with a bulk electrolyte. The proportion of Ca2+ ions in
the channel is greatly in excess of that in the bulk because, in the restr
icted space in the channel, the doubly charged Ca2+ ions require less volum
e and are more effective at neutralizing the charge of glutamates than twic
e the number of singly charged Na+ ions with the same amount of charge.