An SBML (and related XPP and other formats) implementation of the classic HH paper is available in the BIOMODELS database. See far below for links.
XML (web link to model);
XPP (web link to model);
SBML (web link to model)
Schilstra, Maria [m.j.1.schilstra at herts.ac.uk];
Lloyd, Catherine [c.lloyd at auckland.ac.nz]
HODGKIN AL, HUXLEY AF. (1952). A quantitative description of membrane current and its application to conduction and excitation in nerve. The Journal of physiology. 117 [PubMed]