  A discrete multistate kinetic model for water-wire proton transport is
constructed and analyzed using Monte-Carlo simulations. The model allows for
each water molecule to be in one of three states: oxygen lone pairs pointing
leftward, pointing rightward, or protonated (H$_{3}$O$^{+}$). Specific rules
for transitions among these states are defined as protons hop across successive
water oxygens. We then extend the model to include water-channel interactions
that preferentially align the water dipoles, nearest-neighbor dipolar coupling
interactions, and coulombic repulsion. Extensive Monte-Carlo simulations were
performed and the observed qualitative physical behaviors discussed. We find
the parameters that allow the model to exhibit superlinear and sublinear
current-voltage relationships and show why alignment fields, whether generated
by interactions with the pore interior or by membrane potentials {\it always}
decrease the proton current. The simulations also reveal a ``lubrication''
mechanism that suppresses water dipole interactions when the channel is
multiply occupied by protons. This effect can account for an observed
sublinear-to-superlinear transition in the current-voltage relationship.
