Question

It is time to compare and contrast ionotropic and metabotropic receptor mechanisms! First, describe how each type of receptor works. Next, list the differences between the two types of receptors. Then, give an example of a neurotransmitter system that uses an ionotropic receptor to facilitate hyperpolarization, and describe how this works. Finally, name at least one type of sedative drug that binds to this receptor. A complete answer will include the following terms: action potential, binding site, cell membrane, channel, chloride, closed, directly, first messenger, indirectly, ion, ionotropic, inside, metabotropic, neurotransmitter, open, outside, rapidly, receptor, second messenger, slowly.

Answer 1

Ionotropic receptors—are linked directly to ion channels .These receptors contain two functional domains: an extracellular site that binds neurotransmitters, and a membrane-spanning domain that forms an ion channel .Thus ionotropic receptors combine transmitter-binding and channel functions into a single molecular entity (they are also called ligand-gated ion channels to reflect this concatenation). Such receptors are multimers made up of at least four or five individual protein subunits, each of which contributes to the pore of the ion channel.

metabotropic receptors, so called because the eventual movement of ions through a channel depends on one or more metabolic steps. These receptors do not have ion channels as part of their structure; instead, they affect channels by the activation of intermediate molecules called G-proteins. metabotropic receptors are also called G-protein-coupled receptors. Metabotropic receptors are monomeric proteins with an extracellular domain that contains a neurotransmitter binding site and an intracellular domain that binds to G-proteins. Neurotransmitter binding to metabotropic receptors activates G-proteins, which then dissociate from the receptor and interact directly with ion channels or bind to other effector proteins, such as enzymes, that make intracellular messengers that open or close ion channels. Thus, G-proteins can be thought of as transducers that couple neurotransmitter binding to the regulation of postsynaptic ion channels.

	IONOTROPIC RECEPTOR	METABOTROPIC RECEPTOR
	Act Fast	Act slowly
	receptor present	do not have channel
	ligand binding to receptor lead to conformationally change that further create channel through which ion flow	activation of G protein which inturn activate secondary messenger. this ultimately may or may not lead to opening of channel.

GABA γ-aminobutyric acid is used as sedative drug that bind to ionotropic receptors called type A and C GABA receptors and metabotropic receptors called type B GABA receptors

Benzodiazepines, sedative drug act on GABAA receptor and increase the frequency of opening of Cl– channels.

endomorphin and Dynorphin are the drug which act over metabotropic receptor