Question

Fill in the blank with A, B or A and B based on whether the following statements are referring to Ionotropic receptors (A) or metabotropic receptors (B) or both.

a) ___ blocked by a-bungarotoxin

b) ___ their neurotransmitters are encoded directly by genes

c) ___ uses a signal transduction signaling mechanism

d) ___ activation can lead to an EPSP

e) ___ picrotoxin and barbituate binding

f) ___ uses small, clear core vesicles

Answer 1

Receptors are protein-complexes present on the post-synaptic membrane. These can be of two types, namely, ionotropic receptors and metabotropic receptors. The ionotropic receptors allow the influx of ions through ion channels that are present in them. Metabotropic receptors, on the other hand, result in a downstream signaling cascade that results in a slow and long-lasting change in response to the stimulus.

a) Alpha-bungarotoxin is present in the venom of many-branded krait. This acts as an antagonist of nicotinic Acetylcholine Receptors (nAchR). nAchR is an ionotropic receptor. Hence, the answer for this is A.

b) Neurotransmitters that are directly encoded by genes are peptide neurotransmitters. The peptide neurotransmitters can bind to both ionotropic and metabotropic receptors. Hence, the answer for this is both.

c) As mentioned above, signal transduction is a unique property of metabotropic receptors. Therefore, the answer is B.

d) EPSP refers to an excitatory post-synaptic potential. It is produced as a result of an influx of positively charged ions. Therefore, this involves an ion channel. Ionotropic receptors are themselves ion channels. Hence, some of the ionotropic receptors result in an EPSP. Also, metabotropic receptors can be associated with ion channels. Therefore, the downstream signaling from a metabotropic receptor activation can result in the opening or closing of an ion channel that can in turn result in an EPSP. Therefore, the answer is both.

e) Picrotoxin and barbiturates bind to GABA (gamma-aminobutyric acid) A receptors which is an ionotropic receptor. Therefore, the answer is A.

f) Vesicles are small liposomal structures that contain within them neurotransmitters. This holds for both ionotropic and metabotropic receptors. Therefore, the answer is both.