Sensitivity analysis of the β-adrenergic network identifies key system regulators. A) Sensitivity analysis of the normalized-Hill β-adrenergic model. Note the bright green squares prevalent in the phosphodiesterase (PDE), protein kinase inhibitor (PKI), and phosphatase 2A (PP2A) columns, implicating the importance of these three species as key negative regulators of the system. B) Sensitivity analysis of a detailed biochemical model of the same pathway, allowing for direct comparison of the two modeling approaches. A Pearson correlation coefficient of 0.75 was computed between the individual sensitivities of the two models, demonstrating substantial quantitative agreement between the functional outputs of the two modeled networks.