Inositol 1,4,5-trisphosphate receptor (vascular smooth muscle type) (IP₃R)

The **inositol 1,4,5-trisphosphate receptor (IP₃R)** is a large intracellular calcium channel predominantly located on the membrane of the sarcoplasmic or endoplasmic reticulum. In vascular smooth muscle, the type 1 isoform (IP₃R1) is of primary functional significance. IP₃R1 is activated when its ligand, inositol 1,4,5-trisphosphate (IP₃), generated by phospholipase C activity following Gq-coupled receptor stimulation, binds to its cytosolic domain. This binding induces conformational changes that open the channel, releasing Ca²⁺ from the ER/SR into the cytosol. The resulting increase in intracellular Ca²⁺ activates calmodulin and myosin light chain kinase, promoting smooth muscle contraction, thus modulating vascular tone and blood pressure[1][2][3][4][5][6]. IP₃R1 dysregulation contributes to vascular pathologies such as hypertension and heart failure by enhancing maladaptive vasoconstriction or tone. There are three genes encoding IP₃R isoforms, typically forming large tetrameric channels. Selective targeting of IP₃R channels remains challenging due to their ubiquitous expression and structural similarity to ryanodine receptors.

Other names

IP₃ receptorIP3RInsP₃ receptorInositol trisphosphate receptorITPR (gene/protein family)IP₃R1 (most common isoform in vascular smooth muscle)

Ligand activation: IP₃ produced by phospholipase C activation binds IP₃R, causing Ca²⁺ release from sarcoplasmic/endoplasmic reticulum[4][6][9] Drugs/inhibitors: Nonselective inhibitors block channel opening, reducing calcium release Indirect modulation: GPCR agonists (e.g. angiotensin II) stimulate PLC and IP₃ production[3]