Importance of LCC coupling to CRUs demonstrated in SAN cell models with uncoupled Ca _v 1.2 from CRUs (still coupled to Ca _v 1.3) versus models in which CRUs were coupled to both Ca _v 1.2 and Ca _v 1.3. (A and B) Intervalograms of simulated CLs in the partially uncoupled CRU models with uniformly random (A) and square lattice (B) distribution of CRUs, respectively. (C) Results of sensitivity analyses with various Ca_v1.3 percentage in I_CaL for the partially uncoupled models with uniformly random CRU distribution (orange) and square lattice distribution (blue). The results are compared with those of fully coupled models (respective dashed line plots), replotted from Fig. 11 A. Data points are average CLs evaluated between 5 and 16.5 s after simulation onset. Black arrows show the %Ca_v1.3 margin where the models failed to generate APs.