Open-channel-block induced by the neurotransmitter glycine in homomeric alpha1-GlyR and heteromeric alpha1/beta1- GlyR

The strychnine-sensitive glycine receptor (GlyR) is a member of an ion channel superfamily which includes nicotinic acetylcholine, GABAA and serotonin (5-HT3) receptor channels. The highest density of expression is found in the brain stem and spinal cord. There is a high degree of sequence homology between the members of the superfamily, especially regarding the M2 domain i.e. the channel lining domain of the transmembraneous functional receptor channel protein. There are reports on a block of ligand gated ion channels by higher concentrations of the respective neurotransmitters. This could be a molecular mechanism of modulation of the current response to peak doses of synaptic transmitter release. The electrophysiological properties of GlyR are well known for the activation by concentrations of the agonist glycine <1mM. To analyze the effect of the agonist glycine in a higher concentration range in homomeric alpha1-GlyR and heteromeric alpha1/beta1- GlyR we applied 1 mM, 3 mM, 10 mM and 30 mM glycine to small-cells in the whole-cell configuration or patches in the outside-out configuration using the patch-clamp technique. Patch clamp experiments were performed on glycine receptor channels expressed in HEK293-cells. Different electrophysiological parameters, e.g. activation, deactivation and desensitisation were analysed using ultrafast piezo-driven application of test solution. By this approach, we observed a mild decrease of amplitude, an increased rate of current decay in presence of the agonist and a re-opening current after removing the agonist in a dose-dependent manner due to an open-channel-block like mechanism. Similar results were reported for the nicotinic acetylcholine receptor and the GABAA-receptor, but were not documented for the glycine receptor channel so far. Further experiments should elucidate a potential physiological role of this receptor channel property and potential pharmacological modulation.