Mechanisms of the sarcoplasmic reticulum Ca2+ release induced by P2X receptor activation in mesenteric artery myocytes

Background atp is one of the principal sympathetic neurotransmitters which contracts vascular smooth muscle cells (smcs) via activation of ionotropic p2x receptors (p2xrs). we have recently demonstrated that contraction of the guinea pig small mesenteric arteries evoked by stimulation of p2xrs is sensitive to inhibitors of ip3 receptors (ip3rs). here we analyzed contribution of ip3rs and ryanodine receptors (ryrs) to [ca 2+]i transients induced by p2xr agonist αβ-meatp (10 μm) in single smcs from these vessels. methods the effects of inhibition of l-type ca2+ channels (vgccs),ryrs and ip3rs (5 μm nicardipine,100 μm tetracaine and 30 μm 2-apb,respectively) on αβ-meatp-induced [ca2+]i transients were analyzed using fast x-y confocal ca2+ imaging. results the effect of ip3r inhibition on the [ca2+] i transient was significantly stronger (67 ± 7%) than that of ryr inhibition (40 ± 5%) and was attenuated by block of vgccs. the latter indicates that activation of vgccs is linked to ip3r-mediated ca2+ release. immunostaining of ryrs and ip3rs revealed that ryrs are located mainly in deeper sarcoplasmic reticulum (sr) while sub-plasma membrane (pm) sr elements are enriched with type 1 ip3rs. this structural peculiarity makes ip3rs more accessible to ca 2+ entering the cell via vgccs. thus,ip3rs may serve as an intermediate amplifier between voltage-gated ca2+ entry and ryr-mediated ca2+ release. conclusions p2x receptor activation in mesenteric artery smcs recruits ip3rs-mediated ca 2+ release from sub-pm sr,which is facilitated by activation of vgccs. sensitivity of ip3r-mediated release to vgcc antagonists in vascular smcs makes this mechanism of special therapeutic significance. © 2014 institute of pharmacology,polish academy of sciences. all rights reserved.