Which type of receptors are known to increase IP3, thereby increasing intracellular Ca2+?

Muscarinic receptors are a type of G protein-coupled receptor that, when activated by acetylcholine, can lead to the production of inositol trisphosphate (IP3). The mechanism begins with the activation of the Gq protein associated with these receptors. Upon activation, Gq stimulates phospholipase C (PLC), which catalyzes the conversion of phosphatidylinositol 4,5-bisphosphate (PIP2) into IP3 and diacylglycerol (DAG).

The production of IP3 triggers the release of calcium ions (Ca2+) from the endoplasmic reticulum into the cytoplasm. This increase in intracellular Ca2+ can have various physiological effects, such as muscle contraction in smooth muscle cells and modulation of neurotransmitter release in neurons.

This signaling pathway is distinctively associated with muscarinic receptors, particularly the M1, M3, and M5 subtypes, which utilize this mechanism to generate cellular responses triggered by acetylcholine. The other options listed do not typically engage this specific intracellular signaling pathway through the generation of IP3 and subsequent increase in intracellular calcium.