Sukhanova K. Mechanisms of [Ca2+] signalling in artery smooth muscle cells following ionotropic purinergic receptor stimulation.

This study unravels the mechanisms of [Ca2+]imobilisation following P2X receptor activation in arterial myocytes. Ionotropic P2X receptors (P2XRs) are involved in sympathetic control of the vascular tone and mediate Са2+influx into smooth muscle cells (SMCs) leading toplasma membrane depolarization and activation of L-type voltage-gated calcium channels (L-VGCCs). In addition, Са2+ entering the cell may trigger Са2+ release from the sarcoplasmic reticulum (SR) via ryanodine receptors (RyRs). It was recently demonstrated that Ca2+ release mediated by inositol trisphosphate (IP3) receptors (IP3Rs) also provides a considerable contribution to P2XR-linked [Ca2+]iresponses,thus suggesting convergence of metabotropic and ionotropic signaling pathways. Using confocal detection of changes in the intracellular Са2+ concentration ([Са2+]i) and the inhibitors of calcium channels (nicardipine, 5 µM), sarco-endoplasmic Са2+-ATPase SERCA (CPA, 10 µM), IP3Rs (2-APB, 30 µM), RyRs (tetracaine, 100 µM), and phosphalipase C (PLC; U-73122, 2.5 µM), we estimated relative contribution of the above-mentioned four components to the [Са2+]ielevation induced by selective P2XRagonist ??-meATP. We found that relative contribution of Са2+ entry via P2XRs and L-VGCCs the ??-meATP-induced [Са2+]iresponses are comparable. The contribution of Са2+ release via IP3Rs was found to be three times greater than that via RyRs. However, block of L-VGCCs resulted in a sevenfold decrease in the contribution of IP3R-mediated Са2+ release and reversal of the situation. This observationsuggests a functional coupling between activation of L-VGCCs and metabotropic PLC/IP3-mediated signaling cascade. The efficiency of inhibition of ??-meATP-induced calcium responses by PLC inhibitor, on the one hand, and by the IP3Rs blocker and nicardipine, on the other hand, were found to be comparable, whatsupports further the above hypothesis. According to our data, P2XR-linked [Са2+]iresponse results not only from P2XR-mediated Са2+ entry that triggers Са2+ release via RyRs, but also from Са2+ release via IP3Rs activated mainly by L-VGCCs-mediated Ca2+ influx. The latter process,involving PLC-mediated pathway, provides predominant contribution to Са2+ release from the stores after activation of ionotropic purinoceptors.