Glycine is a major neurotransmitter in the mammalian central nervous system.The glycine receptor is a ligand gated Cl- channel, mediating synaptic inhibition in the spinal cord, retina and regions of the brain.The glycine receptor is a pentamer consisting of a and A? subunits.To date there are four known a-subunit isoforms (a1- a4) encoded by different genes.In humans, two alternative splice variants of the glycine receptor a3 have been described: a3L, and a3K where the a3L splice variant bears an additional segment of 15 amino acids within the long cytoplasmic TM3-4 loop. These variants differ in their desensitization kinetics.