Liquid Perfusion Without the Overhead: Fast, Serial Liquid Replacement for PAM Assay Development
Ion channels are a class of trans-membrane proteins prolific in nearly all cell types, with extensive bio- diversity in controlling a vast array of physiological processes from cell-to-cell signaling all the way to homeostasis 1,2. It is possible to separate ion channels into two separate classes: ligand gated and voltage gated. Ligand-gated ion channels (LGICs) represent the class that are activated, or “gated”, in the presence of a ligand, or “agonist”. Functional impairment of LGICs represent a variety of disorders and diseases, and as such they are attractive targets for drug research focusing on various levels of modulation. γ- Amino butyric acid (GABA) activated receptors (GABAA) are chloride conducting channels that function by inhibiting neuronal cell excitability and represent the most abundant inhibitory receptor in the brain3. This receptor has a heteropolymeric structure4 with many identified subunits leading to a high degree of molecular diversity in mammalian species5. With GABA acting as an agonist, other compounds can modulate this evoked chloride current by binding to an allosteric site on the receptor 6. These allosteric modulator compounds are used in various therapeutic treatments including insomnia, anxiety, and, schizophrenia. Allosteric enhancers of channel activity, also known as positive allosteric modulators (PAMs), are major targets for drug discovery and can act either by binding to the extracellular domain or to the pore domain 3. Regardless of their binding sites, PAM activity is only observed in the presence of an agonist and hence their study can be complicated, with multiple serial additions of various compounds needed to properly quantify their effect.