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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 CHANNELS. Trafficking of small charged molecules (ions) thru the cell membrane of neurons determine their ability to signal and respond to each other. The electric charges of ions are in fact responsible for the membrane potential and action potential. But since the cell membrane is almost totally impermeable to ions, there is a need to use specialized cellular devices that can transport ions in and out of the cell thru the membrane. These devices are called ion channels.