Energetics, RR, and magnitude of the control response for agonists co-applied with a negative allosteric modulator. (A) The graph shows the free energy change provided by the inhibitor (ΔG_M) that is required to halve the control response at different magnitudes of the control response (EC_agonist). The black solid line describes the relationship for a fully efficacious agonist that at saturating concentration generates a response approaching a P_A of 1. The red dashed line describes the relationship for an agonist that at saturating concentration generates a response with a P_A of 0.5. The blue dash-dotted line describes the relationship for an agonist that at saturating concentration generates a response with a P_A of 0.25. The calculations were done using Eq. 7. (B) The relationships between the RRs and EC_agonist were calculated (Eq. 8) for the three agonists, assuming the modulator contributes 1 kcal/mol of free energy change.