The graphic shows an example of the receptor response of a ligand-gated ion channel (e.g. GABA). When no ligand is bound, the receptor displays constitutive activity: the ion channel is slightly opened causing a small chloride ion influx.
Addition of a full agonist evokes a change in conformation, which leads to further opening of the ion channel resulting in further hyperpolarisation.Binding of an inverse agonist reverses the constitutive activity and leads to a complete closure of the ion channel. The result is a depolarisation.