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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.
Ion Channel (from outside cell) Tetrodotoxin is the poison that is produced by the puffer fish and a number of other animals. It is a virulent poison, the LD50 for the mouse is 10 nanograms. It acts by blocking the conduction of nerve impulses along nerve fibers and axons. The victim eventually dies from respiratory paralysis.