Far more is known about the muscle-type nic-otinic receptor than about neuronal receptors. One of the reasons for our greater understanding is that a receptor similar to the muscle-type nicotinic receptor is present in great abundance in the electric organ of the Torpedo ray. A large proportion of the surface in the modified muscle tissue in the electric organ is occupied by postsynaptic membrane that contains densely packed, partially crystalline arrays of nicotinic receptors. This has allowed purification (with the help of high affinity li-gands such as a-bungarotoxin), partial sequencing of the receptor subunits, and hence cloning of the genes for these subunits. Tubular crystals of Torpedo receptors embedded in their native lipids can be grown from isolated postsynaptic membranes, and these have been
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