Small molecule G protein-coupled receptor kinase inhibitors attenuate GRK2-mediated desensitization of vasoconstrictor-induced arterial contractions.

Vasoconstrictor-driven G protein-coupled receptor (GPCR)/phospholipase C (PLC) signalling increases intracellular Ca 2+ concentration to mediate arterial contraction. To counteract vasoconstrictor-induced contraction, GPCR/PLC signalling can be desensitized by G protein-coupled receptor kinases (GRKs), with GRK2 playing a predominant role in isolated arterial smooth muscle cells. Here, we utilize an array of GRK2 inhibitors to assess their effects on the desensitization of UTP and angiotensin II-mediated arterial contractions. The effects of GRK2 inhibitors on the desensitization of UTP or angiotensin II (AngII)-stimulated mesenteric third-order arterial contractions, and PLC activity in isolated mesenteric smooth muscle cells (MSMC), were determined using wire myography and Ca 2+ imaging, respectively. Applying a stimulation protocol to cause receptor desensitization resulted in reductions in UTP and AngII-stimulated arterial contractions. Pre-incubation with the GRK2 inhibitor paroxetine almost completely prevented desensitization of UTP- and attenuated desensitization of AngII-stimulated arterial contractions. In contrast, fluoxetine was ineffective. Pre-incubation with alternative GRK2 inhibitors (Takeda compound 101, or CCG224063) also attenuated the desensitization of UTP-mediated arterial contractile responses. In isolated MSMC, paroxetine, Takeda compound 101 and CCG224063 also attenuated the desensitization of UTP and AngII-stimulated increases in Ca 2+ , whilst fluoxetine did not. In human uterine smooth muscle cells, paroxetine reversed GRK2-mediated histamine H 1 receptor desensitization, but not GRK6-mediated oxytocin receptor desensitization. Utilising various small molecule GRK2 inhibitors we confirm that GRK2 plays a central role in regulating vasoconstrictor mediated arterial tone, highlighting a potentially novel strategy for blood pressure regulation through targeting GRK2 function.