PFI-3 induces vasorelaxation with potency to reduce extracellular calcium influx in rat mesenteric artery

Background: PFI-3 is a small-molecule inhibitor that targets the bromodomains (BRDs) of Brahma-related gene 1 (BRG1). This monomeric compound, which has high selectivity and potent cellular effects, has recently been developed. Although PFI-3 has been reported as a potential therapeutic agent targeting thrombomodulin, its role in the regulation of vascular function remains unknown. Therefore, we aimed to investigate the impact of PFI-3 on arterial vessel tone.

Methods: A microvascular tension measurement device (DMT) was utilized to identify alterations in vascular tension within the mesenteric artery. To detect variations in cytosolic [CA²⁺]_i, a Fluo-3/AM fluorescent probe and fluorescence microscope were employed. Additionally, whole-cell patch clamp techniques were utilized to evaluate the activity of L-type voltage-dependent calcium channels (VDCCs) in cultured arterial smooth muscle cells (A10 cells).

Results: PFI-3 exerted a dose-dependent relaxation effect on rat mesenteric arteries with both intact and denuded endothelium after phenylephrine (PE)- and high-K⁺-induced constriction. PFI-3-induced vasorelaxation was not affected by the presence of L-NAME/ODQ or K⁺ channel blockers (Gli/TEA). PFI-3 abolished CA²⁺-induced contraction on endothelium-denuded mesenteric arteries preincubated by PE in CA²⁺-free solution. Incubation with TG had no impact on PFI-3-induced vasorelaxation pre-contracted by PE. PFI-3 reduced CA²⁺-induced contraction on endothelium-denuded mesenteric arteries pre-incubated by KCl (60 mM) in CA²⁺-free solution. PFI-3 declined extracellular calcium influx in A10 cells detected by Fluo-3/AM fluorescent probe and fluorescence microscope. Furthermore, we observed that PFI-3 decreased the current densities of L-type VDCC by whole-cell patch clamp techniques.

Conclusions: PFI-3 blunted PE and high K⁺-induced vasoconstriction independent of endothelium on rat mesenteric artery. The vasodilatory effect of PFI-3 may be attributed to its inhibition of VDCCs and receptor-operated calcium channels (ROCCs) on vascular smooth muscle cells (VSMCs).

Calcium channels; PFI-3; Vasoconstriction; Vasodilation.