Glycine receptors: what gets in and why?

1. The glycine receptor channel (GlyR), a member of the ligand-gated ion channel superfamily, shares many similar permeation properties with the GABAA receptor channel. 2. The GlyR is anion permeable, with PK/PCl < 0.05, has a 5-6 A minimum pore diameter and a permeation selectivity sequence dominated by hydration energies. 3. The channels, which display multiple subconductance states, can be multiply occupied. 4. Two positive arginine rings at the ends of the pore region may contribute to the anion selectivity of the GlyR. 5. Mutation of the extracellular charged arginine ring can impair channel function by decreasing the sensitivity of glycine activation, reducing channel conductance, shifting the normal multi-subconductance states to lower values and by decoupling the link between ligand binding and channel gating. 6. These and other site-directed mutagenesis studies of recombinant GlyR, together with studies of native GlyR, are providing further insights into what controls gating and ion permeation and selectivity through this channel.