The Markov model for competitive antagonism consists of 3 different receptor states, closed (C; yellow), open (O; purple) and desensitized (D; green), which are connected by the specific transition rates for each state.

<p>Because every state can bind up to 3 ligands, which are either agonists (red spheres) or antagonists (blue cones), there are 23 states in this model. Starting at C1, an additional agonist is bound rightwards and an additional antagonist upwards. Contrary to this, the unbinding of agonists and antagonists proceeds in opposite directions. k₁, k_-1, association and dissociation rates of the antagonist; a₁, a_-1, association and dissociation rates of the agonist; d₁, d_-1, transition rates of the desensitized state. Insets: structures of the antagonists used in this study (Tocris).