Ligand-gated channels receptor

The open channel has in most cases a selective permeability, allowing a restricted class of ions to flow,for example Na+, K+, Ca++ or Cl- and, accordingly, these channels are called Na+-channels, K+-channels, Ca -channels and Cr-channels. In contrast, cation-permeable channels with little selectivity reject all anions but discriminate little among small cations. Little is known about the structures and functions of these non-selective cation channels [1], and so far only one of them, the nicotinic acetylcholine receptor (nAChR, see Nicotinic Receptors), has been characterized in depth [2, 3]. The nAChR is a ligand-gated channel (see below) that does not select well among cations the channel is even permeable to choline, glycine ethylester and tris buffer cations. A number of other plasma... 

Nicotinic receptor subunits are part of a large superfamily of ligand-gated channels 202... 

The other ligand-gated channel is commonly referred to as the ryanodine receptor, after the alkaloid ryanodine, which can induce opening or closing as a function of concentration. 

Many receptors for neurotransmitters function as ligand-gated channels for Na and/or Ca " ions (see p. 354). The ones that have been studied in the greatest detail are the nicotinic receptors for acetylcholine (see p. 352). These consist of five separate but structurally closely related subunits. Each forms four transmembrane helices, the second of which is involved in the central pore in each case. The type of monomer and its arrangement in the complex is not identical in all receptors of this type. In the neuromuscular junction (see p. 334), the arrangement aPya8 is found (1). 

Ligand-gated channels, which may either open or close in response to ligand binding. Important examples are the nicotinic acetylcholine receptor, which allows Na into the cell in response to acetylcholine, and the sulfonylurea receptor-associated Kj. channel, which ceases to permit efflux of in response to ATR... 

Several transmitters - acetylcholine, glutamate, serotonin, GABA, and adenosine and its various phosphates - have receptors both among the ligand-gated channels and the G protein-coupled receptors. Thus, these transmitters evidently serve multiple purposes in the nervous system. 

How do ion chaimels, vital to a wide array of biological functions, operate at a molecular level We will examine three chaimels important in the propagation of nerve impulses the ligand-gated channel the acetylcholine receptor channel, which communicates the nerve impulse between certain neurons and the voltage-gated Na+ and K+ channels, which conduct the nerve impulse down the axon of a neuron. 

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