Although the predominant GIRK channels in the CNS are GIRK1/GIRK2 heterotetramers, other combinations of GIRK1-lacking channels, such as homomeric GIRK2 and heteromeric GIRK2/GIRK3, have been described in dopamine neurons of the substantia nigra and VTA, respectively, and play a key role in reward and addiction [42–44]. In light of the absence of GIRK1-lacking channels modulators, Kozek and colleagues conducted a HTS based on a thallium flux assay with HEK293 cells expressing homomeric GIRK2 [45]. This assay led to the discovery of VU0529331, the first synthetic small molecule that activates GIRK1-lacking channels [45]. In whole-cell patch-clamp recordings, VU0529331 increased GIRK2 and GIRK1/GIRK2 currents, though exerting a greater activation in homomeric GIRK2-expressing HEK293 cells (Table 1) [45]. VU0529331 also activated homomeric GIRK4 and GIRK1/GIRK4 channels with micromolar potencies. Given this lack of selectivity, the assessment of VU0529331 effects in cells naturally expressing these different GIRK channels would have been desired, but its low potency (around 5 μM) limited further studies. Furthermore, the authors observed off-target activity on ATP-gated Kir6.1/SUR2a and Kir6.1/SUR2b channels [45]. Nonetheless, the discovery of VU0529331 represents the first step
