Describe the major structural and functional differences between metabotropic and ionotropic receptors - Essay Example

Keywords: Ionotropic, Metabotropic, Neurotransmitter, Ligand The working of the human body depends highly on the action of various neurotransmitters all around the body. Neurotransmitters are chemicals produced inside the body which have the ability to convey signals from a neuron to a target cell across a synapse. The synapse is a cleft like space where neurotransmitters are released from their vesicles and it is here that they bind to different and specific receptors to produce a unique and beneficial effect to the body.

These receptors are protein in nature and are present in the lipid bi-layer of the cell from where they interact with the outside environment. These receptors receive a signal which is then translated into an electrical signal. Based on their structure and mode of action neurotransmitter receptors are generally classified into an ionotropic or ligand-gated receptors and a metabotropic receptors (Iwama & Gojobori 2002, p. 1891). Simply speaking ionotropic receptors are either inhibitory or excitatory in effect as they are stimulated by GABA, glycine, glutamate and aspirate etc (Neurotransmitter Postsynaptic Receptors 1998).

On the other hand metabotropic receptors are neither directly inhibitory nor excitatory. Their function is to regulate the excitatory and inhibitory effects of various neurotransmitters. . The whole receptor is embedded in the cell membrane. It is a pentamer meaning it consists of five different subunits. All subunits are composed of protein and are arranged and aligned in a way that a single pore spanning the whole membrane is created. This setting results in the formation of two different domains; an extracellular and a transmembrane domain.

Ionotropic receptors can be classified according to their neurotransmitters. Generally speaking there are three major categories of ionotropic receptors; cys-loop receptors, the glutamate receptors and the ATP gated channels. On further classification the glutamate receptors are further divided into AMPA (?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid), Kainate and NMDA (N-methyl D-aspartate) receptors (Collingridge et al. 2009, p. 2) The ATP gated family however consists of only the P2X type receptor.

The cys-loop receptors can be classified the furthest. Based on their excitatory and inhibitory effect they can be organized into cationic and anionic receptors respectively. Anionic receptors consist of GABAA, GABAC and glycine receptors while cationic receptors consist of nicotinic acetylcholine receptors and 5HT3 receptors (Connolly & Wafford 2004, p. 529). The working of these ionotropic receptors depends on the endogenous neurotransmitter. The neurotransmitter acts as a ligand. The receptors respond to the presence and absence of ligand by opening and closing the ion pore discussed above.

The binding of the ligand however shows a peculiar change. The endogenous chemical binds to a site on the protein receptor which is different to the site of the ion conduction pore. This allosteric binding is specific to the ionotropic receptors. The receptors and their respective channels are highly