Which secondary messengers are activated by phosphoinositide-coupled receptors?

Phosphoinositide-coupled receptors, also known as G protein-coupled receptors (GPCRs) coupled to phospholipase C (PLC), primarily activate two key secondary messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG). This signaling pathway begins when a ligand binds to the receptor, leading to the activation of the Gq protein. The Gq protein, upon activation, stimulates PLC, which then hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) in the cell membrane to generate IP3 and DAG.

IP3 is responsible for stimulating the release of calcium ions (Ca2+) from the endoplasmic reticulum into the cytosol, further propagating the signaling cascade. On the other hand, DAG remains in the membrane and activates protein kinase C (PKC), which mediates a variety of cellular responses.

The activation of these two secondary messengers is crucial for various physiological processes, including smooth muscle contraction, neurotransmitter release, and many others. Thus, the correct choice reflects the specific secondary messengers that are indeed activated by phosphoinositide-coupled receptors.