Parameters used in the mathematical description of cGMP signaling in MA-10 cells.

VNPR-A was estimated from the initial slope of ANP-induced cGMP accumulation in the presence of 500 μM IBMX. Vmax-PDE and Vmax-PDEs were estimated from data in Figures 7D,E, cell count, and an estimated accessible cell volume of 2 pL. The Km for PDE5 and KI for IBMX were estimated previously, see [49], [50]. The rate constants for phosphorylation and dephosphorylation of PDE5 were based upon the data in Figure 7E. Rate constants of receptor phosphorylation and dephosphorylation and the intracellular concentration of IBMX were estimated from model fits to the data in Figures 7A-C. Initial conditions were steady-state parameter values in the absence of 10 nM ANP and parameters were fit to the data manually.