  We present a novel microscopic tridomain model describing the electrical
activity in cardiac tissue with dynamical gap junctions. The microscopic
tridomain system consists of three PDEs modeling the tissue electrical
conduction in the intra-and extra-cellular domains, supplemented by a nonlinear
ODE system for the dynamics of the ion channels and the gap junctions. We
establish the global existence and uniqueness of the weak solutions to our
microscopic tridomain model. The global existence of solution, which
constitutes the main result of this paper, is proved by means of an approximate
non-degenerate system, the Faedo-Galerkin method, and an appropriate
compactness argument.
