Summary

In the glycine-bound forms the channel allows hydrated chloride ions to pass. However, when strychnine is bound this channel is restricted so that it is too narrow for even a dehydrated chloride ion to fit. The responsibility for this change falls on the M2 helices, which tilt and rotate. An outward movement of the helices from the strychnine-bound state to glycine-bound state increases the radius at both constriction sites. A smaller rotation in the glycine/ invermectin-bound state cause's constriction at Pro266 such that hydrated chloride ions cannot pass. 

Figure 5.

Channel restricting M2 helices viewed parallel to the membrane displaying their movement between the different bound states. The channels inner surface is also shown in white allowing visualization of both restrictions sites.

Cryo-EM has allowed for the high resolution elucidation of GlyR structure, provoking  development in our understanding of its molecular interactions - an essential step in understanding the regulation of inhibitory neurotransmission.