This paper reviews the main theoretical approaches proposed to underst
and ion permeation in gramicidin, a model for more complex biological
ion channels. Continuum and molecular dynamics viewpoints have contrib
uted to significant insights in the essential transport mechanisms. Th
e focus is on the recent semi-microscopic approach which analyzes the
microscopic single file aspects of the system without neglecting the l
ong range macroscopic effect of both solvent and membrane.