Schematic diagram of the coupled human atrial myocyte/fibroblast paradigm which forms the basis of this study. (A) One human atrial myocyte was coupled to one fibroblast modeled according to (MacCannell et al., 2007), and assuming a gap junctional conductance, Ggap of 0.5 nS. The total capacitance of the human atrial myocyte is 50 pF and the capacitance of the fibroblast is 6.3 pF. (B) A schematic of the fibroblast which incorporates five active membrane conductances. The voltage-gated currents are a background Na+ current, Ib,Na; two K+ currents, IK1, and IKv; the Na+–K+ pump current INaK. INP represents the novel ligand-gated transient receptor protein (TRP) channel current which is activated by natriuretic peptide. (C) The I–V curve for the natriuretic peptide-induced conductance in the fibroblast. Note, the linear relationship having a reversal potential near 0 mV.