It is recognised that some receptors appear to “pop” in and out of an active con

Question

It is recognised that some receptors appear to “pop” in and out of an active conformation in the absence of agonist binding. In the developing brain, this is important as certain receptors won’t be used for some time but are still present and therefore the fact that they occasionally adopt an active conformation prevents them from being targeted for destruction. Speculate on how this ability to form the active conformation sporadically makes these receptors the target of heterologous desensitisation. As part of your answer, define the phrase “heterologous desensitisation”.

Explanation / Answer

Answer

Heterologous Desensitization is a Receptor (biochemistry)-based phenomenon in which one receptor type, when bound to its ligand, becomes unable to further influence the signaling pathways by which it regulates cells and, in the case of cell surface membrane receptors, may thereafter be internalized; the desensitized receptor is degraded or freed of its activating ligand and re-cycled to a state where it is again able to respond to cognate ligands by activating its signaling pathways.it leaves a cell transiently unresponsive to agents that activate the desensitized receptor but not to agents that activate other receptors. It commonly occurs with G protein-coupled receptors where it is mediated by the G protein-coupled receptor kinases (GRK) and arestins that are mobilized during the receptor's activation. Homologous desensitization also occurs with cytokine and other types of receptors such as those of the epidermal growth factor receptor type but in these cases desensitization is mediated by other types of receptor kinases. Homologous desensitization serves to limit or restrain a cells responses to stimuli. However, some stimuli cause cells to active protein kinase Cs which act to desensitize multiple types of receptors thereby rendering a cell unresponsive to agonists of multiply receptor types. This commonly occurs with G protein coupled receptors cytokine and other non-G protein couple receptor types may also become heterologously desensitized by agents which activate protein kinase C but, perhaps more commonly, by agents that activate other protein kinases such as mitogen-activated protein kinase (p38 MAP kinase). Heterologous desensitization may also occur in cells that are grossly over-stimulated for prolonged times by a certain agents.

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