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The channel has a large diameter of 0.8x1.1nm, and is non-selective for small ions. However, it has an upper exclusion size limit corresponding to molecular weights of about 600 Dalton of permeants. Because most metabolites have molecular weights lower than 600 Da and have been shown to pass through porin channels, porins are called general diffusion pores.
All ionotropic receptors have similar protein structures consisting of a complex of 4-5 proteins that assemble to form a quasisymetrical cylinder or ion poer. Each subunit protein spans the membrane 3-4 times and it is these TM domains that make up the ion channel portion of the receptor.