Ca2+ channel-sarcoplasmic reticulum coupling: A mechanism of arterial myocyte contraction without Ca2+ influx

Laboratorio de Investigaciones Biomédicas, Departamento de Fisiología and Hospital Universitario Virgen del Rocío, Universidad de Sevilla, E-41013, Seville, Spain.
The EMBO Journal (Impact Factor: 10.43). 10/2003; 22(17):4337-45. DOI: 10.1093/emboj/cdg432
Source: PubMed


Contraction of vascular smooth muscle cells (VSMCs) depends on the rise of cytosolic [Ca2+] owing to either Ca2+ influx through voltage-gated Ca2+ channels of the plasmalemma or receptor-mediated Ca2+ release from the sarcoplasmic reticulum (SR). We show that voltage-gated Ca2+ channels in arterial myocytes mediate fast Ca2+ release from the SR and contraction without the need of Ca2+ influx. After sensing membrane depolarization, Ca2+ channels activate G proteins and the phospholipase C-inositol 1,4,5-trisphosphate (InsP3) pathway. Ca2+ released through InsP3-dependent channels of the SR activates ryanodine receptors to amplify the cytosolic Ca2+ signal. These observations demonstrate a new mechanism of signaling SR Ca(2+)-release channels and reveal an unexpected function of voltage-gated Ca2+ channels in arterial myocytes. Our findings may have therapeutic implications as the calcium-channel-induced Ca2+ release from the SR can be suppressed by Ca(2+)-channel antagonists.

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    • "While most vascular smooth muscle expresses all 3 known RyR isoforms (RyR1–3), it is primarily the activation of RyR1 and RyR2 that regulates excitation–contraction coupling [2]. These receptors are activated by Ca 2+ , and can act as amplifiers of smaller Ca 2+ signals caused by Ca 2+ influx or inositol 1,4,5-trisphosphate (IP 3 )-mediated Ca 2+ release [3]. This amplification, called " Ca 2+ induced Ca 2+ release " (CICR), mobilizes large amounts of SR Ca 2+ into the cytosol and has been proposed to serve an important role in excitation–contraction coupling in smooth muscle [4]. "
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    ABSTRACT: Ryanodine receptors (RyR) are Ca(2+)-sensitive ion channels in the sarcoplasmic reticulum (SR) membrane, and are important effectors of SR Ca(2+) release and smooth muscle excitation-contraction coupling. While the relationship between RyR activation and contraction is well characterized in arteries, little is known about the role of RyR in excitation-contraction coupling in veins. We hypothesized that RyR are present and directly coupled to contraction in rat aorta (RA) and vena cava (RVC). RA and RVC expressed mRNA for all 3 RyR subtypes, and immunofluorescence showed RyR protein was present in RA and RVC smooth muscle cells. RA and RVC rings contracted when Ca(2+) was re-introduced after stores depletion with thapsigargin (1μM), indicating both tissues contained intracellular Ca(2+) stores. To assess RyR function, contraction was then measured in RA and RVC exposed to the RyR activator caffeine (20mM). In RA, caffeine caused contraction that was attenuated by the RyR antagonists ryanodine (10μM) and tetracaine (100μM). However, caffeine (20mM) did not contract RVC. We next measured contraction and intracellular Ca(2+) (Ca(2+)(i)) simultaneously in RA and RVC exposed to caffeine. While caffeine increased Ca(2+)(i) and contracted RA, it had no significant effect on Ca(2+)(i) or contraction in RVC. These data suggest that ryanodine receptors, while present in both RA and RVC, are inactive and uncoupled from Ca(2+) release and contraction in RVC.
    Cell calcium 11/2012; 53(2). DOI:10.1016/j.ceca.2012.10.006 · 3.51 Impact Factor
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    • "The endothelial murine cell line (EOMA cells, ATCC catalog no.: CRL-2586) derived from a mixed hemangioendothelioma was cultured at 37°C and 10% CO2 in DMEM with 4.5 g/L glucose, supplemented with 4 mM L-glutamine and 10% fetal bovine serum (BioWhittaker, Belgium). Primary cultures of pulmonary artery smooth muscle cells were obtained following previously described protocols [23]. "
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    ABSTRACT: Aquaporin-1 (AQP1) is a water channel that is highly expressed in tissues with rapid O(2) transport. It has been reported that this protein contributes to gas permeation (CO(2), NO and O(2)) through the plasma membrane. We show that hypoxia increases Aqp1 mRNA and protein levels in tissues, namely mouse brain and lung, and in cultured cells, the 9L glioma cell line. Stopped-flow light-scattering experiments confirmed an increase in the water permeability of 9L cells exposed to hypoxia, supporting the view that hypoxic Aqp1 up-regulation has a functional role. To investigate the molecular mechanisms underlying this regulatory process, transcriptional regulation was studied by transient transfections of mouse endothelial cells with a 1297 bp 5' proximal Aqp1 promoter-luciferase construct. Incubation in hypoxia produced a dose- and time-dependent induction of luciferase activity that was also obtained after treatments with hypoxia mimetics (DMOG and CoCl(2)) and by overexpressing stabilized mutated forms of HIF-1α. Single mutations or full deletions of the three putative HIF binding domains present in the Aqp1 promoter partially reduced its responsiveness to hypoxia, and transfection with Hif-1α siRNA decreased the in vitro hypoxia induction of Aqp1 mRNA and protein levels. Our results indicate that HIF-1α participates in the hypoxic induction of AQP1. However, we also demonstrate that the activation of Aqp1 promoter by hypoxia is complex and multifactorial and suggest that besides HIF-1α other transcription factors might contribute to this regulatory process. These data provide a conceptual framework to support future research on the involvement of AQP1 in a range of pathophysiological conditions, including edema, tumor growth, and respiratory diseases.
    PLoS ONE 12/2011; 6(12):e28385. DOI:10.1371/journal.pone.0028385 · 3.23 Impact Factor
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    • "Indeed, L-type Ca2+ channels have recently been demonstrated to exhibit metabotropic actions following membrane depolarization. In particular, they appear to be linked to PLC-coupled G proteins enabling IP3-induced Ca2+ release (IICR) from internal stores, which has been termed Ca2+ channel-induced Ca2+ release38, 39. Thus, in addition to the Ca2+ inward current, Ca2+ channels may serve as voltage sensors even in the absence of any Ca2+ influx. "
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    ABSTRACT: Depolarization-induced contraction of smooth muscle is thought to be mediated by Ca2+ influx through voltage-gated L-type Ca2+channels. We describe a novel contraction mechanism that is independent of Ca2+ entry. Pharmacological experiments were carried out on isolated rat gut longitudinal smooth muscle preparations, measuring isometric contraction strength upon high K+-induced depolarization. Treatment with verapamil, which presumably leads to a conformational change in the channel, completely abolished K+-induced contraction, while residual contraction still occurred when Ca2+ entry was blocked with Cd2+. These results were further confirmed by measuring intracellular Ca2+ transients using Fura-2. Co-application of Cd2+ and the ryanodine receptor blocker DHBP further reduced contraction, albeit incompletely. Additional blockage of either phospholipase C (U 73122) or inositol 1,4,5-trisphophate (IP3)receptors (2-APB) abolished most contractions, while sole application of these blockers and Cd2+ (without parallel ryanodine receptor manipulation) also resulted in incomplete contraction block. We conclude that there are parallel mechanisms of depolarization-induced smooth muscle contraction via (a) Ca2+ entry and (b) Ca2+ entry-independent, depolarization-induced Ca2+-release through ryanodine receptors and IP3, with the latter being dependent on phospholipase C activation.
    Acta Pharmacologica Sinica 09/2009; 30(8):1123-31. DOI:10.1038/aps.2009.98 · 2.91 Impact Factor
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