Gq alpha subunit

It gets released into blood vessels and binds alpha-1 receptors on the smooth muscle.

Alpha-1 is a GQ receptor.

GQ turns on phospholipase C, which makes IP3, and IP3 releases calcium stores from inside the muscle cell.

Calcium binds chymodulin, which switches on myosin light chain kinase.

That lets myosin pull on actin and the muscle contracts.

The alpha subunit of the G-protein complex is bound to GDP, but when activated binds to GTP, causing conformational change and downstream signalling to occur.

Depending on the type of G-protein coupled receptor, GS, GI or GQ, the downstream messengers will either alter in their nature or activity.

GS receptors stimulate adenylate cyclase to increase cyclic AMP, while GI receptors do the opposite.

GQ receptors activate phospholipase C and DAG, as well as calcium.

The advantage of G protein-coupled receptors is that they can produce signal amplification via downstream signalling, and that many cellular actions can be achieved via single stimulus.

An example of a GS receptor is the beta-1 adrenergic receptor.

An example of GI is an opiate receptor.

and GQ is an alpha-1 receptor.

Vasopressin, when used as a vasopressor, binds to V1 receptors.

These are GQ-coupled, G-protein-coupled receptors, leading to an increase in intracellular calcium within the smooth muscle of the vascular tree, leading to vasoconstriction.

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