Which receptors are known to increase IP3, thus increasing intracellular Ca2+ levels?

The receptors that are known to increase inositol trisphosphate (IP3), leading to an increase in intracellular calcium levels, are the alpha-1 adrenergic receptors. These receptors are coupled primarily through Gq proteins, which activate phospholipase C (PLC). When PLC is activated, it catalyzes the breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2) into IP3 and diacylglycerol (DAG).

IP3 then diffuses through the cytoplasm and binds to IP3 receptors located on the endoplasmic reticulum, which triggers the release of calcium ions into the cytosol. The increase in intracellular calcium can lead to various cellular responses, including muscle contraction and neurotransmitter release.

In contrast, the other receptor types (alpha-2, beta-1, and beta-2) have different signaling pathways and do not primarily lead to increased levels of IP3 or intracellular calcium in the same way that alpha-1 receptors do. Alpha-2 adrenergic receptors are generally inhibitory and tend to decrease cyclic AMP (cAMP) levels, while beta-1 and beta-2 adrenergic receptors primarily act through Gs proteins, leading