Figure 2
The response level of the functional-HOTSM has three plateaus. A first response-plateau, FP, in the absence of ligands is equal to 1/[1+ 1/(L)]. A third response-plateau, TP, at high agonist concentrations is given by 1/[1+1/(L·a·b·d)]. Finally, a second-response plateau, SP, at intermediate ligand concentrations is dependent on all 7 parameters. The three plateaus may be above, at, or below each other, panels A-D, rendering dose-response curves that are positive or negative co-operative, bell-shaped or terraced, as well as reverse bell-shaped or reverse terraced. Parameter values in panels A-D were arbitrarily chosen in order to demonstrate several aspects of the model. AS varied in three steps from 10-2 (------) to 102 (-·-·-·-·) by a factor 100 in panels A and B, while AM varied in three steps from 0.3 (------) to 3000 (-·-·-·-·) by a factor 100 in panels C and D. The remaining parameters were fixed. Thus in panel A: L = 1/4, AM = 20, a = 100, b = 0.01, c = 0.01, and d = 17. In panel B: L = 4, AM = 20, a = 10, b = 0.01, c = 0.01, and d = 0.7. In panel C: L = 1/4, AS = 1, a = 100, b = 0.01, c = 0.01, and d = 17. And in panel D: L = 4, AS = 1, a = 10, b = 0.01, c = 0.01, and d = 0.7.